WowAce

OneChoice tries to help you reduce quest reward choices down to, ideally, one choice.

Keeps track of space left in your bags.

Enables user defined sounds for Party, Guild, Raid and Custom Channel chat messages.

Good looking, smoothy and helpful nameplates

Acolyte2

Displays the time remaining before your (temporary) pet is dismissed.

IncomingHealsLib

RaidAgent

Guilder brings common guild-raid tasks together in one convenient place.

Shows the spec of people around you in the tooltip.

Death reports

Fires events whenever a raid member "fails."

FuBar_PetInFu

Configuration library

Prospecting and Disenchanting Aide

Square Minimap and more

Healer gear benchmark

Heads Up Display with Player and Target Info

Considers an item against all the items you have to determine whether or not it is an upgrade

Monitors the combatlog identifying players from the oposite faction near you.