WowAce

Keeps track of HoTs, DoTs, Buffs and Cooldowns. With audio and text alerts to refresh them.

Queing of /who and SendWho() queries and a much better interface (see docs), with gurantee to be executed & callback.

StatLogicLib

Configurable Castbars

SacredBuff

FlexBar2

Friends list improvements: notes, remembering the information of offline friends, friend list syncing and backups, and a fuba...

Incubator

Library providing mappings between trade skill recipes, spells and created items

Reduces interface tedium by doing the little things for you.

Sells all junk in your inventory at once.

Show buffs on nameplates.

Watches your chat, flagging missplled words, and offering correctly spelled suggestions.

cyCircled

Food/water macro generator

An extension to the default WoW Unit Frames.

Violation

Improved Questing Experience

Display Cooldown Count of Spell Icon and Item

CT_RaidAssist style raid frames