WowAce

PreferredItems

HiveMind

FuBar_VolumeFu

Adds a button to your character and inspect window that shows a summary of gear enchants and gems.

One-click smart mounting.

ArenaPointer

Tells you if you're buffed

InstanceMaps

Options for TinyTip

Adds four icon indicators to Grid (top, bottom, left and right).

For Developers (of Addons which uses LibWho-2.0): show queues and queries in realtime

Gives equipped and overall iLvl to indicate the quality of a character's gear.

RaidSpy

Creates a broker plugin for all your broker launchers

Reverse Engineering will drill down and search your tradeskills for their elements

Lets you drag UI frames around

Announces results of readychecks to the raid/party, installs "/rc" alias, shows rc timer bar

Displays info about who rolled Need/Greed/Pass on items that are currently rolled for

Cartographer_Routes

Speeds up triggering actions such as items or spells by triggering them on key/mouse down rather than release