WowAce

Clean looking square minimap with many options.

Displays the zone level ranage of the zone you are in and also gives you a suggest zone and instances to be in.

Allows you to prevent addons from sending and receiving messages.

Scorchio!

lugMD

CharScanner scans Basic Character Data, Talent Specifications, Equipment, PvE/PvP Achievements, PvE Boss Kill Statistics and ...

Displays friend notes in unit tooltips, at logon, and in /who results.

aUF_RangeCheck

A library to return spell duration and debuff type of a spellID.

Shared handling of media data (fonts, sounds, textures, ...) between addons.

A library to help with localization of classes.

ShadowGreenLight helps you decide if recasting SWP/Corruption is worthwhile

Show coordinates on minimap

Toggles player names.

Pet Theory

Monitors for friendly deaths and announces them as in Myth: The Fallen Lords

AceBuffGroups

Shows activity for hidden ChatFrames by making their tabs flash.

Provides more visible access to dungeon and raid difficulty settings via FuBar.

MobHealth