WowAce

Raid cooldown assignments for healers

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

Adds Blizzard, oRA2, oRA3, CT_RA MainTank or Dungeon Finder Tank icon (shield or MT, 1, 2 ... 10) or text (MT or MT1, MT2 ......

Adds AFK status to Grid frames.

Adds Name and Buyout Price sort columns to the auction house.

Sets you to DND when you fight a boss, and some other crap.

Addon management panel extreme release edition

Adds the "pixel perfect" font "Visitor" to LibSharedMedia

obRaidAssist

changes LFR wing descriptions to encounter lists

Diplomat

A library which provide tools for detecting adverse effects on units.

Shows on the minimap where to fetch Finklestein's reagents

Automatically sends guild recruitment ads to the GuildRecruitment channel.

Customizeable UI to display the values tracked by AbsorbsMonitor

Really very early stage. No, earlier than that.

Shows the duration of the most recent (or current) combat

Shift-clicking on a user name in chat shows a tooltip with their whois information.

Opacity effect on action buttons in cooldown.

Takes a screenshot when you kill a boss or gain an achievement