WowAce

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

FuBar_HBFu

Very very simple tooltip

ClosetGnome_Tooltip

autoLFG

Mute all sounds except boss emotes and addon sounds

A simple buff remover.

A library to convert ItemId to ItemId of player's faction

Tracks if the target does NOT have the tracked DOT.

MarkMyTarget

Printing unknown AddonPrefixes to your chat

GetDKP_AutoPost

Displays the remaining time on grid icon's cooldown animation.

Automatically swaps between weapons and lances.

Assistace for Blackhand (Mortar warning in P2, custom says for bombs and marks in P3)

Envenomous

Adds tooltip for debuffs (and other things? you found out: no).

Creates an Auctionator's shopping list with all recipes your alts need based on Altoholic data.

Shared handling of media data (fonts, sounds, textures, ...) between addons.

KivinPetHappiness