WowAce

Monk Brewmaster/WindWalker Priority and Buff/Debuff Tracking Tool

Adds aura indicators to unit frames

Hotkey interface for spells, macros, other clickables.

Filters AFK and DND messages after you've seen them once.

Add-on that shows which battle pets can be farmed this week

Saves Auction House search queries.

Shows the price of a single item in the Auction House.

Visual Raid Cooldown Tracking

Color manipulation library.

Adds talent specialization role status to Grid.

Uses guild notes to add alts' main names to chat windows and other places

Adds a Friendly Fire mode and data collection to Skada.

ClassColors

Collects, analyzes and presents information about the virtual economy.

Adds 3 indicators to each side (top, bottom, left and right).

Display an arrow that points to a raid/party member anchored to raid frames

Whats

Friends & Guild Data Broker plugin.

Tracks whispers and conversations

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