WowAce

Better minimap blips

Shows a countdown bar for the duration of auras (e.g. HoTs, DoTs)

View party member quest logs

Tool for easy task assignments in raids.

FuBar_RicoXPFu

Helper addon for the Zul'Drak daily "Troll Patrol: The Alchemist's Apprentice"

Show a bar indicating the remaining lifetime of your temporary pet

A FuBar plugin for MagicMarker

ERP

A DPS Data Broker plugin.

Pick Pocket Countdown Timer for Rogues.

Displays an animated bar with next enemy swings

DKP ingame management

Adds information to Titan Panel about your Professions and opens ProfessionsBook

Enables cooldown notification between players and allows party members access to each-others spell books.

Saves who searches in a favorites list.

Announces results of readychecks to the raid/party, installs "/rc" alias, shows rc timer bar

Keeps track of your reagents.

Simple embeddable publish-subscribe implementation.

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