WowAce

Uses linear regression and a log of hitpoint values to estimate how long a boss has left to die and reach execute range.

Minimal KoS-list-addon

Debuff Monitor: A Powerful & Configurable Raiding Tool

Congratulate people when they ding

ShammySpy

Makes it very easy to collect rare battle pets.

TrainingWheels

AntiInvite

Write event handlers in a simple GUI in-game

Hides the Order Hall Command Bar

Adds predicted lists for spells while the user types

Add TomTom Waypoints for Flight Masters in classic

Joins the LFG channel automatically.

Adds easier gear switching to FuBar.

New/Old BG indicator, Join by ID, Quick Leave Queue, etc.

SliceWatcher

Displays a variety of useful stats for tanking

Alert your friends when you ding, get an achivement, or get phat lewts!

Adds notes to item tooltips

Colors friends/bg score board/who list names by class color