WowAce

Lists and/or reminds people missing flasks or food buffs at every ready check.

Keeps track of people who have recently sent you messages.

Congratulate people when they ding

Social tracking suite.

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

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

ChatAssist2

MiniChat

A mod to filter the Trade chat, shunting it to a seperate chat window if it exists (chat window is OMGWTFBBQ).

Shift-clicking on a user name in chat shows a tooltip with their whois information.

Converts incoming ALL CAPS CHAT into lowercase text.

Assistace for Blackhand (Mortar warning in P2, custom says for bombs and marks in P3)

Waitlist addon with EPGP Mass Award hooking.

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

Converts commonly used acronyms into hyperlinks.

Allows communication to be shared across realm through Battle.net.

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

ViewAddonMessage

Send Mail to Groups

Provides bang-whispers for your professions.