WowAce

Adds a simple percentage threat status to Grid.

See all incoming casts on your target. Also includes resurrection monitor. Uses libhealcomm-3.0 and librescomm-1.0

Shows you which bosses you've killed next to the raid finder frame.

oUF_HolySmurf

Sets you to DND when you fight a boss, and some other crap.

ChatAssist2Options

A Latency Data Broker plugin.

Menagerie

Shows who controls Wintergrasp and the time until the next battle.

For Developers (of Addons which uses LibWho-2.0): show queues and queries in realtime

Hunter 'Misdirection' activity and cooldown monitoring for raids/groups. 'Readiness' aware.

ElectrofluxTextronator

Reports the total threat on a mob at the end of combat.

Scaffold

Colors friends/bg score board/who list names by class color

Filters unimportant Buffs.

oUF element for highlighting debuffs that are dispellable by the player

NielasAran

Allows communication to be shared across realm through Battle.net.

A simple addon that warns you if your pet isn't attacking while you're in combat.