WowAce

Shows skills in a tooltip and allow them to be used. Also keeps track of Cooldowns.

Necronomicon2

GrindStatus

Sells all junk in your inventory at once.

Checks your gear before bosses and yells at you if you're an idiot

Try on different gear and see their total stats and their differences. In short, an ingame CT-Profiles-like addon.

GotWood

A collection of Rogue modules.

SacredBuff

Manufac

SRA

Shows skills in a tooltip and allows them to be used.

Switch macro depending on zones or BigWigs boss modules.

WhoDrop

UnitActionBars

Show item durability and quality in the character frame.

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

Visualises healing.

FuBar_HonorFu

Reduces interface tedium by doing the little things for you.