WowAce

BlizUF_LMH4

A simple buff remover.

Tells your party members when you interrupt stuff, or fail to do so.

Filters unimportant Buffs.

Synchronise friends among your characters

LibRockModuleCore-1.0

Displays how much your Shield Barrier will absorb if it is used at any given moment.

Adds Debuff Highlighting to oUF.

Database of reforging IDs

DrugTest

LDB display of the players current damage percent modifier

Printing unknown AddonPrefixes to your chat

KivinLootzor

MorgBid

ManufacSnoop

Gives equipped and overall iLvl to indicate the quality of a character's gear.

Check for unenchanted and ungemmed items

RareCaller

With Mists of Pandaria Blizzard publish all characters from an account unless you disable that 'feature'. This addon warns you.

Standalone LibUnitID, with runtime diagnostic utilities