WowAce

Give whispers an instant messenger feel.

Chat addon, filtering messages and UI changes

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

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.

A friendly companion that remembers the chat.

Redirect character errors, system messages and information messages.

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

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

Lightweight Chat Improvements

A blizzard group finder replacement

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

Prat

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

Loudmouth

Displays online guild mates.

Displays online friends.

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

A Simple World of Warcraft Spam Filter!

Says random things in chat when casting any spell or ability. Type "/ss help" for the user's manual.