[quote="mellored"]

A human being's made of more than air
With all that bulk, you're bound to see him there
Unless that human bein' next to you
Is unimpressive, undistinguished
You know who…

Cellophane
Mister Cellophane
Shoulda been my name
Mister Cellophane
'Cause you can look right through me
Walk right by me
And never know I'm there…

This guide assume you know the details of stealth.  If you don't, or have questions about it, check out the rules of the hidden club.
[/quote]

[quote="mellored"]  Just the numbers:
Nothing fancy, just a list of stuff that gives bonuses to stealth. 

Training: Pretty obvious, but it gives +5.  Backgrounds are a great way to add this to non-stealthy classes.  Some races can get it too.

Dex: The skill is based of it, giving up to a +10 boost.  It's also a great stat, giving you AC, and initive.

Armor/Shield: You can take a penalty, though likely you'll be using Dex, so you won't need the heavy stuff.
 

ED's
+2 to Dex  Not even thief of legends gives an actual boost to stealth.

  Numbers to beat

Actual numbers are all over the place.  So this is my rough estimate of the monster's skills. (if you have a better estimate, let me know).

Easy DC = 50% of the monsters.
Medium DC = 75% of the monsters.
Hard DC = 100% of the monsters.

Add 10 to auto-beat passive.
Add 20 to auto-beat maximum.

vecna has the highest at +34 (followed by 32).  Thus 43 (passive), and 53 (active) are the most ever needed.  (You also need to get around blindsight.)

Dex (9) + training (5) + level (15) = 29.  You should hide 60% of the time.

Add a background (2) and racial bonus (2) = 33.  You should hide 80% of the time.

Add skill training (3) and an item (6) = 42.  Enemies will have to actively look for you.

Add untraceable (5), and take a ED to bump dex (1), and grab the assassins cloak = 48 (roll twice)  Vecna has a .0114 chance of noticing. (.0038 or less for others).

[/quote]

[quote="mellored"]
Getting Hidden

Terrain/Lighting:  Which is totally DM depenant.

At-Wills and properties.
Cunning Rogue (class feature) Move a little to upgrade concealment to total concealment.  It can be improved to work for a shorter distance.
Evermeet Warlock (warlock PP) Only works against a few targetes, and requires a teleport, but it starts you with none.  However, they arn't too hard to pick up, and the more you get (such as monk's fallen needle + staff of the traveler + movement boosters + planestrider boots), the better this is.
Thief of Legends (ED) Basicly gives you perma-invisibility.  However, it's only as a level 30 feature.
Persistent Tail (stealth 10) Due to some poor wording, this upgrades your cover.  Needs a cooperative enemy (or ally).
Elusive Hexer (eladrain, warlock, fey pact) Requires a hit, and only last till the end of the current turn.  Though most warlocks will have concealment to stay hidden.
Gathering Night (feat dusk elf stealth) Turn concealment into invis with a standard.
Psionic Veil (psion 27) Need to hit, and only 1 enemy, but it allows several to hide.
Eyebite (warlock 1) Only 1 enemy, and you need to hit.
Veil of the Mind's Eye (battlemind 23) Need to hit, some distance, and only works against 1 enemy.
Emerald Scale Concealment (feat dragonborn, assassin) Not much here, unless your recycling dragon breath.
One with Shadows (Shade racial) Let's you hide with any cover, including allies.  However, the standard action is extreamly costly.
Elixir of Invisibility (consumable 6+) Cheap way to get invisible as a minor, but it's uncommon.
Lesser Elixir of Invisibility (7) Why the "lesser" is more expensive i have no idea.  But they do thet same thing.

Encounters, dailies, and conditionals.
Shadowflow Armor (23+) Encounter invis as a minor.  Pretty nice considering it's the main source of untyped stealth bonus.
Cloud of Darkness (drow racial) Easy way to get stealth.
Hidden Lore (binder) Invis for dropping someone, which can turn up often.
Stalk the Senseless (psion epic) Psions have a few spamable dazing powers.
Greater Ring of Invisibility (ring 23) minor for invis.
Fade Away (gnome) invis as a reaction.  This can be buffed a bit.
Delbanian Vambraces (arm 23) Crit's or kills cold powers give you invis, possibly for the encounter if you don't mind some damage.
Assassin's Cloak (assassin feat) Normaly you can just move to hide while invis, but if you invis off turn, or invis on a hit, there's definatly uses for this.
Cloak of Invisibility (23+ rare) Possible encounter long invis, though it takes a standard to start.
Feytouched Armor (12+) Encounter invis as a standard.
Ring of Invisibility (ring 18, rare) Another encounter invis, but as a standard.
Chameleon Ring (ring 16) Let's you stealth without ANY cover.  Useful for some situations.

Staying Hidden

Terrain/Lighting:  Which is totally DM depenant.

At-Will, and properties
Killer in a Crowd (feat, assassin 11) Due to some poor wording, this just flat out gives cover.  Of course, many DM's may disagree, and thus make it horrible as the enemy your hiding behind can just point you out.
Shadowband (ring 27, rare) Perma-concealment.  No if's, and's, or but's.
Master Thief (Thief PP) You don't get revealed by attacking.  Most DM's won't like it, but if you find a nice spot, you can kill everything without being noticed.
Drawn Shadows (feat assassin paragon) Always on assuming you have an enshrouding candle.  If not, it's still useful.  Note that enshrouding candle can makes it easy to guess your square (in the middle of the darkness).  Also, if you want to be cheesy, say there's darkness in your backpack.
Shadow Blend (warlock 2) Same as Drawn shadows (get an enshrouding candle) , except you don't get it on your own turn, or when stunned.
Shadow Walk (warlock) Moving is a pretty easy requirement.
Phantom Chaussures (boots 18) Shadow Walk, the item.
Cursed Shadow (feat assassin, warlock) Shadow walk, the MC feat.
Shadow Dancer (PP) In a round about way, this upgrades concealment to total concealment.  But it's really not good for getting hidden in the first place.  Invis after an OA isn't shabby either.
Ghostwalker (monk PP) If you CA, you have concleament.  If your hidden, you have CA.  Combo with Nethermancy (mage 10) to just have it.
Mark of Shadows (feat) Remain hidden on a miss.
Armor of Dark Deeds (leather 14+) Attack with CA, and you have concealment.
Shadow Stride (rogue 10) Move from cover, across the open, back to cover without loosing stealth.
Cloaked Sniper (rogue PP) Missing let's you stay hidden, and shift, but requires concealment/cover.
Shadow of the Wild (feat) Conditional, and with a penalty, but it let's you hit and stay hidden.
Stone Heart Spirit (feat, shaman, world speaker) Mobile cover.  Combo's fantasticly with Fading Spirit.
Darting Shadow (assassin 6) Being able to jump from cover to cover is nice.
Enshrouding Candle (wonderous 7) Dim light normaly provides concealment against normal vision.
Twilight Torch (shade 6) Gives you dim light, but cost a minor.  Enshrouding candles are generally better.
Ever-Fading Armor (10+) Basicly adds (sustain standard) to any invisibility.
Transcendent ki focus (feat) Requires hitting with a teleport power, and only last till the start of yoru turn.

Encounter, dailies, and conditionals
Rogue Attack Powers Some let you remain hidden. Distracting Shot (1, cunning), Shadow Strike (1), Shadow Steel Roll (3), Fitting Demise (13), Strike of Dancing Shadows (13), Perfect Sniper (27).
Dishonorable Tactics (rogue 16) Adds "remain hidden" to any power.
Greater Ring of Invisibility (Ring 23) After a milestone, it's almost as good as a shadowband.
Ranger Attack Powers Only 1 "remain hidden".  Stalking Strike (3)
Watcher of Vengence (avenger PP) 1 "remain hidden".  Hidden Dager (11).  Though +2 to stealth.
Sandstorm Weapon (any 8) when you drop someone.
Stalker's Armor (hide) let's you keep concealment for an extra turn.
Piwafwi (neck) Daily for Concealment till you attack/are hit.  Note that this is not until the end of the enounter.  So if your careful, it could possibly last all day.
Smoke Snake (10 consumable) Cost a standard, but it last the encounter.
Blackshroud Weapon (10+) Strictly worse then sandstorm (unless you're attacking an ally, but that's bag-o-rats).

Movement 

Anything that let's you shift (paticularly as a free action after an attack) can get you into stealth (assuming you can hide there).  I'm not going to list every movement option, but here are some ones that work well.

Move action: Simply attacking then moving works.

Feats:
Mark of Finding  Helps keep you adjacent to an enemy, so you can punish/OA.
Mark of Sentinel  Any OA.    Very nice for those aiming to stay hidden in battle.
Mobile Warrior (feat fighter 21): Shift after most weapon attacks.
Ghostwalker Style (deft strike, effectivly) Free action after the attack.
Purple Dragon (Theme) hit with an MBA.
Opportunity Sidestep (11) After you hit with an OA.  Worse then mark of sentinal/mobile warrior, but more readily availible.
Storm Blade Channeling (storm sorcerer, SBC)  hit, arcane ranged (in melee).  Storm sorc's are dex.
Staff of Travel (con 13) Divine melee.
White Lotus Master Evasion (11, WLE) Arcane at-will hit only.  Consider Eldrich Strike.
Predatory Magic (razorclaw) Close arcane only, which limit's it use as an OA.
Silent Shot Phantom/Midnight Blade Whisperer (rogue feat) Adds shift to a few powers.
Criterion of Balic Practice (martial) Adds shift to a few powers.
Power of Trickery (Divne) Adds shift to a few powers.
Secret Recovery (drow) After a saving throw.
Wildblood Speed (warden, wildblood) Shift when marked enemies ignore you.  Which would be pretty good, (hide->punish->shift hide) if warden had any use for Dex.
Desert Moon Student Adds shift to a few powers, but only 1/2 the time.
Wild Virtue (bard) Hard to control, but it can show up often.
Stout-Handed Staff (small) If you can knock prone as an OA, this works.

Items:
Boots of chaiphon (feet) you take a little damage, but minor action shift.

Other:
Guardian Counter (theme) Yup, you can shift 2, stealth, take the attack (at -5) then counter attack.
Fallen Needle: (Monk at-will) Shift as a minor.  Not a bad pickup for any half-elf.

Countering Special Senses.
Truesight (117 creatures) v Blindsight (199 creatures):   (316 total)This may be the same thing as blindsight.  Depending on how you read the rules.  It just say's "see blindsight".  
Nothing counter's truesight.

Walls: Ok, i lied, you can still sneak around a wall or other line of effect blocking stuff.  Which can be place by the DM, or summoned via a few spells.  But that also means your not close to the action.

Adept of Whispers (invoker PP) Invoker is an odd place.  But you flat out are immune to blindsight AND tremorsense .  Tack on +2 for stealth for fun.
Elude Senses (stealth util 2) Minor, encounter, 1 turn.  Though it cover's tremorsense and darkvision as well.
Grayflower Perfume (Consumable 10) Minor, 1 turn.
Reflexive Psychic Shroud (scar rare 7+) It's a daily, and only for a turn, though covers tremorsense as well.

Tremorsense (206 creatures):  Note that this does not need line of effect, or line of sight.  So walls won't help.
Flight (movement)  There are many ways to gain flight.  Including a potion, boots, PP's, or armor.
Pixie (Race) Deserves special mention since they start with flight.  Doubly so since they are stealthy.
Lightstep Slippers (boots 21) Immunity with a +5 stealth, a quality choice.
Scorpion Carapace Armor (Scale, Plate +4) An decent alteritive.

Entering your square.

You will always be noticed if an enemy enter's your square.

The first option is simply to not be run over.  If you hide behind a defender, or stay in the air, there's little chance of you being noticed.

The second best spot is hide is in their square.  They would have to move out, and back to notice.  This is a major advantage of pixies, but small races can still to it to large monsters, and medium can do it to bigger.  It has the added advantage of helping to give you OAs.

The other option is to take an immidiate "run away" powers, such as Acrobat's Escape.  Polearm gamble could would work nicely too.[/quote]

[quote="mellored"]
Bonuses While hidden.

Enemy needing to guess your square Best possible defense is not being attacked.
Total Concealment +5 defense vs Melee and ranged: Next greatest defense is not being hit.
CA A little more offense never hurts (unless you want to miss).

Items:
Shadowmaster Ki Foucus  large extra damage
Sehanine's Mark of the Dark Moon (boon) 1/2 damage, none on a miss.
Shadowdancer's Gloves  extra damage
Serpentine Bracers extra damage, and the poision keyword.
Ghost Dance Weapon +2 defense for a turn, you probably won't need defense.

Feats:
Fading Spirit (gnome shaman) Hidden for your spirit.
Feyborn Stratagem (gnome, 11, warlord) CA for your allies with warlord powers.  Better if you intentionally miss with band of fellows.
Hidden Insight (assassin, shrouds) Let's you load up for a nice first turn attack.
Silent Shot Student (ranger/rogue) Some nice bonus damage for the quintisential hidden at-will.
Spirits of Stealth (gnome, primal) extra damage vs bloodied.  It's alot, but it's also a feat bonus, and only works 1/2 the time.
Unseen Dread (gnome, psion) slide 2.

PPs:
Champion of the Vigil Crit on 19-20, and a reroll.
Darkstrider (ranger) 3+Wis damage.
Guild Executioner (executioner) +4 to hit your first attack of the encounter.
Shadow Dancer Stay invisible for a turn after an OA, or immidiate action.  Also does a fair bit to keep you hidden.
Verdant Stalker (rogue) Basicly +1.875 to sneak attack damage (assuming d8's).  Though a more liberal reading allows it to apply to all damage rolls, which could be a fair bit of damage (+.75 per d4, +.5 per d6).
Death Arrow (seeker, bloodbond) -2 to hit and better crits, but only with ranged (not AOE) against enemies adjacent to your target.  Nice bonuses, but it's gunna be hard to use without help.[/quote]

[quote="mellored"]
Ways to use it.

Surprise Round:  It's like a free action point, that you have to use at the beginning of comabt.  Somewhat conditioinal, but it comes at very little oppertunity cost.

Scouting: Knowlage is power.  If your fighting fire giants, you can take the time before battle to drink a few fire resist potions.  Covers RP applications as well.

Defense: While it does alot for your own saftey,  spending resources to hurt your allies isn't a good thing.  Unless…

Defender Punishment:  You can punish enemies for ignoring you.  Just make sure your punishment is strong enough to compinsate (or possibly negate) enemies attacking a squishy.  A few great things would be the hospitaliter PP, Weaknening challenge, Lure of Iron + Prescient Retaliation, or mark of stroms to slide on a fighter/warden to move the enemy away from the ally.

OA's:  You can position yourself so when enemies move, or make a range attack, they give you an OA.  Though you need to coordinate with your allies to get enemies to provoke, OA's can be quite potent (two-weapon flurry, helm of oppertunity, weapon of great opportunity, ect..).

Sneaky Utility: While you have to "be quite", and can't "attack" nothing in the rules say's utility powers are loud or flashy (though your DM may disagree).  So feel free to pop those heals, slide allies, grant saving throws or whatever.  Fading Spirit + Assistance of the Strong Spirit can be extreamly fun RP.
[/quote]

[quote="mellored"]
Combos and examples.
 

[/quote]