WowAce

ClosetGnome_Mount

OneView

LibDataBroker plugin showing some random XP related data

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

A library to handle rearrangement of blizzard's frames when bars are added to the sides of the screen.

Sniff

Instant PROC notification

Dailies Quest Tracker

A fully featured library tracking all ongoing absorb effects

Fancy up the PlayerPowerBarAlt frame

BankItemsFu

Toolset for tanks, providing information on taunts and other valuable information.

Doodle

Automatically invites player from templates.

GridAlert

RotLatency keeps track of your reaction to cooldown expiration.

Automatically sells low quality gray items and selected white items to the vendor.

Make it easy to explain bosses in Raids.

Keeps tracks of /rolls.

Generate a macro with random mounts