WowAce

Automatically equip 'Chef's Hat' if the Chef enters the kitchen (Cooking TradeSkill).

Dailies Quest Tracker

RotLatency keeps track of your reaction to cooldown expiration.

Saves Auction House search queries.

Allows for easy congratulating when someone earns an achievement.

PartyToGo

AnchorsAway

AbacusLib

Adds Raid Target Icon status to Grid (Player or Player Target).

Auto sizes frame layout depending on group/raid size or predefined zone data

Display combo points for Arcane Blast debuffs

MultiTips

LibGUIFactory-1.0

Tracks specialization and talent data for group members

HealComm-2.0

Toggle Windowed Mode with click or keybind.

Handles the assignment, coordination, and announcement of many parts of the Lich King encounter in Icecrown Citadel.

OneChoice tries to help you reduce quest reward choices down to, ideally, one choice.

InstanceMaps

Right-click on minimap blips to open a targeting menu (out of combat).