WowAce

Information display for Hunters.

Doodle

Allows you to create icons, which can be customized greatly by user's input. CiR is more than just the usual cooldown tracker.

Keeps track of gold and cash flow across multiple characters

Notifies you of experience gains

Control screenshot format and quality via LDB displays

Automatic tracking of the current target's creature type. For the discerning PvE hunter.

Hemlock

OneView

Keeps track of healing spells cast by everyone in a group.

SinkLib

Cartographer_Mailboxes

A simple range indicator for optimizing Halo damage.

Tracks profession specific cooldowns and items across all your characters

Simple oRA3 Maintank Target Frames, based on oUF

A frame designed for each specialization of druid's watching their main power and important buffs/debuffs

GemCensus inspects people and records which gems they have socketed. Then displays which gems are the most popular.

RotLatency keeps track of your reaction to cooldown expiration.

Puts a timer in /yell when you get Unbound Plague during the Heroic Professor Putricide encounter

Quest helping: fetching items to use, that sort of thing.