WowAce

Keeps an eye on someone's distance from you, and alerts you if they get too far.

Adds a third text indicator to Grid.

Action button layout and configuration

oUF_HolySmurf

Displays Currencies as a Data Broker source

Make the unit frame fade if out of range.

Toolbox-1.0

Really very early stage. No, earlier than that.

Simple, nice-looking power bar addon for all classes.

DKPmon

MountLib

Provides training reminders to help decipher the Blizzard Spell Alerts.

Improvements to the standard Blizzard Eclipse bar for balance druids. Use /ebp for the config screen.

Reports the total threat on a mob at the end of combat.

Provides the the health and target of by an unit targeted mob (meant to be used for tanks).

Monitors AP when dots are applied, clearly showing current vs applied AP levels.

Simple and rich Death Knight rune customizations

Spy on your guild.

A library to provide tools for formatting money and time.

Allows for gold tracking across multiple time frames