WowAce

A 'channeling spell'-tracking addon for Affliction Warlocks. Drain Soul, Drain Life/Harvest Life and Malefic Grasp.

This addon helps with daily quests.

Enhances the Equipment Manager to let you control the helm/cloak visibility for each set.

Langoustine

A library that maintains a cache of items and their types.

Wrapper to convert HealComm data from 3.0 to 4.0

A lib to manage action bar and timers

Menagerie

SacredBuff_Mounts

Add in keybindings to place raid marks on mouseover, or the target if there is no unit being moused over

An attempt at giving a complete overview of Arena battles

Helps to track outgoing mails

UnitActionBars2

Notifies the raid when someone is Dazed.

Paparazzi

Light-weight enhanced casting bars

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

Bag and item management utilities

Keeps an eye on someone's distance from you, and alerts you if they get too far.

Allows combined aura detection. motw + gotw, all 4 mage int buffs, etc. in one status.