WowAce

Capsule

DaPortrait

SEasyRotation

Plays amusing sounds whenever you skin a mob

FuriousTask

Assistace for Blackhand (Mortar warning in P2, custom says for bombs and marks in P3)

PoisonSwapper automatically manages weapon swapping for maximum DPS

Flames anyone who lets his debuff expire on Malygos Phase 3

Shows a money overview for your current realm in the tooltip on the money in your bags

Enables cooldown notification between players and allows party members access to each-others spell books.

Mail plugin for any DataBroker display.

Crush Chance

Show a bar indicating the attack power gained from Vengeance.

Replacement for WoW's flash/fade functions.

FuBar_KungFu

Lists and/or reminds people missing flasks or food buffs at every ready check.

A frame with a text that gives you the amount absorb left on target, or in TankMode absorbs left on yourself.

Lets you drag UI frames around

nRaidTracker

Show a bar indicating the unit's Holy Power count.