WowAce

Manages social information with a focus on main-alt associations.

XRS

ArcHUD2

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

Visualises healing.

Violation

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

Displays online friends.

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

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

StarTip (Tooltips from Outerspace)

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

Barks at you when you target a crowd-controlled unit

Alternate Power- and Combopoint/SoulShard/HolyPower-bar

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

A replacement tradeskill window for Classic

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

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

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

Configure triggers to send messages to your raid team such as timers, rotations, and health/power based triggers. Raid smarter not harder.