WowAce

Tells you who bought your auctions.

Wardrobe2

Adds indicators to the sides of Grid frames.

LDB display for Oak Interrupts Broker

lugMD

A Mount and Companion manager

AltClick an item in your bag to add it a mail, auction, or trade frame, and alt-click to buy a stack if reagents.

Make it easy to explain bosses in Raids.

Uses guild notes to add alts' main names to chat windows and other places

CharScanner scans Basic Character Data, Talent Specifications, Equipment, PvE/PvP Achievements, PvE Boss Kill Statistics and ...

A library to try to guess a level of a player.

Buffalo

Flames anyone who lets his debuff expire on Malygos Phase 3

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

A superior broker/LDB display for users of the Recount damage-meter.

Aspect checker addon for Hunters.

World of Warcraft Classic addon to display current zone information.

Lets you drag UI frames around

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

Doodle