WowAce

Suppresses chat messages from damage meters and provides single chat-link damage statistics in a popup.

Simple library that handles multiple levels of logging.

Visual loot monitor

Jigsaw

PetBar

Draws some lovely 3D portraits in the standard Blizzard artwork.

Displays online guild mates.

SanityItemCache

Client for MagicDKP which handles standby calls and bidding on items.

FuBar_OutfitterFu

Priority 3 loot announce addon

Mapster's Minimap brother

Considers an item against all the items you have to determine whether or not it is an upgrade

Add lines to ore and gem tooltips that show prospecting sources/results.

BuffMe

ShadowGreenLight helps you decide if recasting SWP/Corruption is worthwhile

Questing minion

Short EPEEN

RBM

SurgeonGeneral