WowAce

Makes the Battle Objectives Frame movable

SmartFitter

UIThing

Notifies you of new calendar event invites and reminds of upcoming events on all characters and realms

FuBar_LootTypeFu

Show a bar indicating the attack power gained from Vengeance.

RaidMarshal

Destruction Warlock priority module for clcInfo -- Maighurl

End of combat reporting for feedback on how your cast time was spent or wasted.

RC4Lib

Records special in-game moments; Achievements, Reputation Gains, Level Ups, Battleground & Arena Wins, so you never miss one ...

Sets you to DND when you fight a boss, and some other crap.

BalerocHealers

Converts commonly used acronyms into hyperlinks.

Keeps an eye on someone's distance from you, and alerts you if they get too far.

Raid cooldown assignments for healers

Alert your friends when you ding, get an achivement, or get phat lewts!

CryptoLib

Tools to easily compare gear among party members.

Chat frame tweaking module for TweakHub.