WowAce

Configure triggers to send messages to your raid team such as timers, rotations, and health/power based triggers. Raid smarter not harder.

Displays information about the current zone on the World Map

Queing of /who and SendWho() queries and a much better interface (see docs), with gurantee to be executed & callback.

A framework for chat ehancement modules.

Another HUD addon

Changes the look of the default UI

A powerful, comprehensive utilty for displaying graphics and information based on buffs, debuffs, and other triggers.

Tracks Raid/Instance/World Boss lockouts for all your characters, daily/weekly quests, currencies, trade cooldowns, and more!

In-game EPGP guild helper, supports standby, main/alt shared pools, minEP, offpecGP. Fixed price list with progress multiplier.

Inventory Management with virtual bags divided into sections.

Bulk mail sending made really easy

Allows you to view all items from all your characters on the same account, when-ever and where-ever you want.

A modular, lightweight and screen-estate saving grid of party/raid unit frames

Priority 3 loot announce addon

Arena unit frames

GDKP gold run ledger

A library to provide information about zones and instances.

Instant PROC notification

A Simple World of Warcraft Spam Filter!

A replacement tradeskill window