WowAce

FuBar_SoulJarFu

Babble-2.2

Role playing AddOn that shows extra information about characters as entered by the player.

Raid Frames using the oUF framework.

Tracks vulnerability debuffs on multiple mobs

Adds custom effects to your cursor.

Sheppard

Auto and random summon highly customizable for your pets and mounts, with Data Broker support.

Regain that wasted space!

Tracks SendAddonMessage Spam

Threat-2.0

Adds two icon indicators to each corner (total: 8 icon indicators).

Display an informational fighter jet style HUD while flying or riding

Automatically and immediately cancels all in-game cinematics and movies

Mutt (Macro Update Target Tool) provides slash-commands that can patch the predefined targets in your macros.

TabletLib

Incoming Heals

Separate indicator for your HoTs with timer.

Allows tradeskill usage by clicking items or reagents.

Shows skills in a tooltip and allow them to be used. Also keeps track of Cooldowns.