WowAce

Combat log replacement

AspectsBar

Lists and/or reminds people missing flasks or food buffs at every ready check.

SmartyCat

Notifies you of experience gains

Selectively loots your fishing catches.

Omnibus

A DPS Data Broker plugin.

Allows movement and scaling of class-specific resource displays

Tracks whispers and conversations

Litmus

Puts a timer in /yell when you get Unbound Plague during the Heroic Professor Putricide encounter

DaHud

A library that tells wether a item is a quest item or not (equipped or in bags)

LDB broker for group interrupts

FuBar_uFriends

Building a Better Mailbox

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

Audible Alerts for self-gain, self-lost, any-gain, all-lost of statuses.

LDB data source for herb, ore and skinning node data