WowAce

Tracks the HoTs you cast.

XRS

Checks your gear before bosses and yells at you if you're an idiot

Visualises healing.

Barks at you when you target a crowd-controlled unit

Violation

Shows the mirco menu and game menu in a clickable broker tooltip.

StarTip (Tooltips from Outerspace)

A replacement tradeskill window for Classic

Automatically leaves the global channels when inside an instance/raid and restores them when exited.

Compact & customizable filtering, monitoring and grouping of buffs and debuffs

Says random things in chat when casting any spell or ability. Type "/ss help" for the user's manual.

Adds a highlight border to items in your MogIt Wishlist, making them easier to see.

Add-on that shows in a unit tooltip window a number of killed mobs of the same kind

Displays information about the current zone on the World Map

Alternate Power- and Combopoint/SoulShard/HolyPower-bar

Displays online friends.

Provides quick access to information on your group and their equipment, enchant and gem choices.

Shows where the equipment of inspected users or yourself is from.

Add item levels to Inventorian