WowAce

Shows guild and system message of the day only if either one of them has changed since the last login.

nRaidTracker

Provides extended aura status settings.

Provides training reminders to help decipher the Blizzard Spell Alerts.

FuBar_ExitFu

Converts incoming ALL CAPS CHAT into lowercase text.

FuBar_PetFu

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

Bag and item management utilities

Nudge

Shows loot information in item tooltips

Adds icons to the configuration menu for all standard Grid indicators.

Show a bar indicating the unit's Holy Power count.

A helper addon for the achievements "Let It Snow", "Fistful of Love", "Shake Your Bunny-Maker", "Check Your Head", and "Turkey Lurkey"

Collects and displays census information. This AddOn is licenced under the GNU GPL, see GPL.txt for details.

Vox

"Your quest log is full". How many quests do you have in your log?

EquivalencePoints

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

Adds Blizzard, oRA2, oRA3, CT_RA MainTank or Dungeon Finder Tank icon (shield or MT, 1, 2 ... 10) or text (MT or MT1, MT2 ......