WowAce

A Mount and Companion manager

EnchantList

Sneakily inspect how much gold your mouseover target has made so far.

A Perl layout with oUF.

Gives equipped and overall iLvl to indicate the quality of a character's gear.

A tool to appraise, estimate, or judge your equipment against the equipment of others.

FuBar_ChatAlertsFu

Tells you who bought your auctions.

ClosetGnome_Fishing

Building a Better Mailbox

SpyGnome

Mutes Annoying Sounds

Records mail when visiting the mailbox to make keeping track of mail and expiration dates easy.

Avion

Displays info about who rolled Need/Greed/Pass on items that are currently rolled for

Shows optimal target to use various area healing spells

What actual item level is an item? Yes, it's horrible we need a library for this.

Draws some lovely 3D portraits in the standard Blizzard artwork.

Battleground Timers in a HUD around the Blizzard BG status

Relays item drops to your guild chat.