WowAce

Am I locked out? - Displays all RaidIDs for all chars

Displays the remaing cooldown of the action you tried to use

Floating Combat Text of awesomeness. Caw. It'll eat your crackers.

Numerical and graphical display of Combo Points and similar buffs/debuffs. Also tracks Holy Power and Soul Shards.

Cleans up minimap buttons and makes them accessible through a pop out menu!

Food/water macro generator

Bayi's Extended Questlog

Add-on that shows which mounts can be farmed this week

XP bar using Ace3.

Display auras on action buttons.

Aloft

Database of item upgrade IDs

Show item durability and quality in the character frame.

Item stat breakdown, analysis and comparison

Reports on a configurable dashboard or to group chat on consumables, buffs, AFK, mana and many many others but in an intellig...

QuestLog

Adds custom effects to your cursor.

Assessment

Find five Ephemeral Crystals, get a pink hippogryph

A library to provide a markup syntax