WowAce

Scan for rare mobs so you can find them and their loot

Library providing multi-column tooltips.

Show the transmog appearance of an item when you mouse over it, and shows collection-status in bags, shops, and elsewhere. Works on transmog, mounts, pets, and decor.

Simple and super light-weight tracking of profession links for all your alts.

StarTip (Tooltips from Outerspace)

Lightweight but powerful auction house interface

Item stat breakdown, analysis and comparison

Collectinator is an addon which will scan your pets and mounts and provide information on how to obtain them.

Complete tradeskill information.

Tooltip of awesomeness. Moo. It'll graze your pasture.

A fancy LDB reputation display, show faction reputation and reputation change history

Adds various information based on PeriodicTable to item tooltips.

Set and manage character notes that are displayed in unit tooltips and /who results.

Kaliban's Class Loot List Star Display

Provides shareable notes and other information for your guild, party and raid community.

Dynamic item DKP calculation

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

Displays item durability and repair cost.

This will keep track of how much you have paid per item in your inventory. Only one of (Auctionator, Auctioneer, AuctionLite,...

Healer gear benchmark