WowAce

Tells your party members when you interrupt stuff, or fail to do so.

Closes chat when the player is instead trying to move

Records special in-game moments; Achievements, Reputation Gains, Level Ups, Battleground & Arena Wins, so you never miss one ...

FuBar_CRDelayFu

AntiInvite

Broker launcher plugin for Blizzard Equipment Set

Adds 4 text indicators to the Grid frames.

Bind a key to cycle through party members

SCT_Cooldowns

Mute all sounds except boss emotes and addon sounds

Tracks money/tokens across all your characters; /goldwatch for options.

Printing unknown AddonPrefixes to your chat

Applies LibKeyBound to Spell Book and Macro UI Buttons.

Displays how much your Shield Barrier will absorb if it is used at any given moment.

Inventory Management

Easy Button for casting MD/ES/ToT etc on tanks.

Provides cooldown timers for abilities you want to track

Tracks your crits.

FuBar_GrindFu

Adds tooltip for debuffs (and other things? you found out: no).