WowAce

Makes tracking reputation much simpler. By InSo(v)nIaX

Shows at-a-glance what raid buffs/debuffs you have.

Raid target control and instance shortcuts for Broker

Assist you with faction transfers letting you know which mounts, spells, etc you have and what they will be swapped to.

HealComm-2.0

Library to provide visual bar creation and management.

Track of your tradeskills across characters, create small buttons for them and track cooldowns.

Facilitate better communication for loot councils

JostleLib

Interface-central mount management

Shows a money overview for your current realm in the tooltip on the money in your bags

Shared handling of media data (fonts, sounds, textures, ...) between addons.

SacredBuff_Mounts

A library to provide tools for formatting money and time.

LDB launcher for Grid/Grid2

Aggro Warning System for Parties and Raids.

GirlFriend

Provides quick notification (sound and visual) of your tanking status of your current target. Meant for tanking.

InstanceMaps

A simple visual combat log with spell/skill icons for Classic WoW