WowAce

Status indicator that shows if a unit is hostile (probably mindcontrolled)

A library that maintains a cache of items and their types.

RapidCast

Improved Guild Control Panel

TickTo

Continously scan for addons using excessive CPU - especially bursts

Show order resources and troop counts in the Order Hall minimap icon tooltip.

An experience bar for classic that shows the entire process from 1-60

Fixes the TradeSkill search bar

Hold a key to temporarily center and magnify the Minimap.

Auto confirms Roll & Loot

Calculates the relative value of attributes towards physical dps.

CrossRealm

Displays a table for possible outcomes of incoming hits with their probability

Yikes

Keeps an eye on someone's distance from you, and alerts you if they get too far.

Experience is an addon that helps you evaluate another player's dungeon experience.

Reduce the chance that talent switch be forbidden.

FuBar2

Managing and viewing loot-type rolls