WowAce

Allows you to prevent addons from sending and receiving messages.

Enables user defined sounds for Party, Guild, Raid and Custom Channel chat messages.

A customizable view of friends and guildmates.

Creates new chats with guild channel functionality

Generates and posts random Chuck Norris facts to a specified chat medium.

Uses guild notes to add alts' main names to chat windows and other places

Privacy2

Shows activity for hidden ChatFrames by making their tabs flash.

Simple language selection for Data Broker

Don't underestimate your little critters!

Captures chatframe Tradeskill Links for later reference in an easy to read format

Enables you to see Chinese, Japanese and other languages in game

Filters AFK and DND messages after you've seen them once.

Automatically leaves the global channels when inside an instance/raid and restores them when exited.

Adds your name to chat messages

TwiCo

DreamChat

Improved Quest Tracker

Enables cooldown notification between players and allows party members access to each-others spell books.

vChat