WowAce

HUD that you can tweak the way you want.

Inspects all members of raid and saves in database, as well as lists people's dkp values

Wowhead Data dump for GatherMate

Displays the locations of the chests for the Treasure, Treasure Everywhere achievement

FuBar_HonorFu

Displays the remaing cooldown of the action you tried to use

Quest History tracker and shows lists of quests in each category

Cryolysis 2

Regain that wasted space!

Displays online guild mates.

Smart mount randomization on a button! Empty coconut halves not included.

Displays Pet Info for Hunters and Warlocks. Also keeps track of Stables and Pet and Demon skills.

Death analysis tool

Cartographer_Treasure

Achievements

manipulate the minimap in numerous ways; move, scale, skin.

Gears skins for Masque.

Litmus

A library to help with localization of item types and subtypes.

GotWood