WowAce

Chat addon, filtering messages and UI changes

Scan for rare mobs so you can find them and their loot

Give whispers an instant messenger feel.

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

Shared handling of alternate identity data between addons.

Enables multi-line/unlimited-length pasting of text or commands into WoW

A friendly companion that remembers the chat.

Set and manage character notes that are displayed in unit tooltips and /who results.

Redirect character errors, system messages and information messages.

Watches your chat, flagging missplled words, and offering correctly spelled suggestions.

Blocks Chinese Chat

A blizzard group finder replacement

Lightweight Chat Improvements

A simple slash-command-based addon for querying item information from the Blizzard servers via ItemIDs and SpellIDs.

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

Displays online friends.

Displays online guild mates.

Manages social information with a focus on main-alt associations.

Prat

Mutes various chat related annoyances while in capital cities and instances.