WowAce

Mutt (Macro Update Target Tool) provides slash-commands that can patch the predefined targets in your macros.

Friends & Guild Data Broker plugin.

Keeps track of your reagents for buffing.

Cartographer_Herbalism

Pins on the World Map for quests you have not completed yet

Simple library that handles multiple levels of logging.

LilSparky's Workshop mod for Trade Skills

Raid Cooldowns

Volume control panel.

Reduces interface tedium by doing the little things for you.

Tools for MultiBoxers or Group questing/leveling

Allows tradeskill usage by clicking items or reagents.

Prompts for canceling of pet battles if no rare pet is found in the opposing team.

Tracking and ranking of dps/hps in a guild.

QuestAnnouncer

Raid Frames using the oUF framework.

Smooth group roll frames

ItemBonusLib

Adds a button to your character and inspect window that shows a summary of gear enchants and gems.

Database of FlightMaster locations for HandyNotes