Cladhaire needs your help!!!

[Karrion]

Cue shameless self-promotion: My addon Poisoner is mainly useful for Rogues (though it can be used by other classes as well).

On my Warlock ShardAce in invaluable.

[tophero21]

rogue: stunwatch, tick

[Dridzt]

Warrior(tank):
Satrina's CombatMonitor (post-combat incoming damage breakdown, to see if my mitigation is suffering someplace in particular),
Grayhoof's Scrolling Combat Text , Barryj SpellAlertSCT (Blizz can imitate but can't replicate the original),
SorrenTimers ,
Gello's ItemRack (fast gear switching),
Cirk's Targetz (who is targetting what indicator on tooltip),
Cirk's Ammocheck (you can't pull without ammo),
Iriel's RedRange and WatchCombat (toc update needed) (get early warning when a party member stumbles on a creep),
Ashenstaff LifeAlert (party getting damaged notification).

Not listing general use mods like sRaidFrames, Ora2, BigWigs although I use those too but not related to the class specifically.

Another personal favorite is WankooMP3 (also not class related )

Edit: Links added

[Tekkub]

Well, it is class-specific, but can be used by everyone... ImbaPalas!

[robthedude]

SHAMAN - TotemManager (also known as Chaman, a french guy wrote it but it has english locale) hands-down the best totem addon I've found

[Cladhaire]

Thanks guys, keep it coming. Anyone have any suggestions regarding Necrosis, Cryolysis, Serenity, etc. and that whole slew of addons? Do you find them useful? Does someone? Should I cover them?

Is Sprocket around anymore?

[Tekkub]

I've not seen a replacement for sporcket.. and damnit I want one. I hate "always on" bars, pop-spheres kick much more ass.

[Auralei]

For Druids:

Druid Bar
Grid(really for all healers)

Shaman:
GotWood?

Warlock
Grimoire Keeper

[Bouvi]

Mage
Cryolysis
FuBar_ReagentFu
SmartDebuff (Part of SmartBuff)
Frosty

Rogue
Natur EnemyCastBar is good for timing your kicks
FuBar_AmmoFu for tracking your throwing quantity
RogueSpam
Poison Master

Priest
Clique for casting spells
SmartDebuff (Part of SmartBuff)

Hunter
Natur EnemyCastBar - Hunter timers
FuBar_AmmoFu
Fizzwidget HuntersHelper
Fizzwidget Feed-O-Matic

SmartBuff for all of them

[PathMaster]

Every shaman needs a reincarnation timer that displays the number of ankhs left. I use: FuBar AnkhTimerFu
I second Grid for healers.
I also nominate Visual Heal
for healers.
I also wonder if Henge is ready for Primetime yet? A necrosis like mod for all classes and ace based as well.

[ravagernl]

Shaman's : YATA

Druids: Druidbar ofc

[Firedancer]

Paladin: PallyPower , SmartBuff/SmartDebuff

some also like HolyHope (pala-fied necrosis I think)