WowAce

Keeps track of space left in your bags.

SpyGnome

Shows Status Bars that you can drag around and group up for your cooldowns

Displays item durability and repair cost.

Provides shareable notes and other information for your guild, party and raid community.

Proximo

AspectsBar

A library to provide a clean dropdown menu interface.

Necronomicon2

Henge

Deathknight Rune Display

FuBar_ExperienceFu

Provide plenty of links

LittleTrouble

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

Tracks skill and tradeskill costs and progressions, as well as trainer locations.

Loot Distribution System

Quickly see what counter-combinations your epic followers cover and which ones are likely to get a new combination when rerol...

Numen

ItemSync the happy item gatherer and toolkit.