WowAce

Shows skills in a tooltip and allow them to be used. Also keeps track of Cooldowns.

Marks the locations of Hallow's End candy buckets on the worldmap and minimap.

A replacement tradeskill window for Classic

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

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

QuestLog

Reports in raid chat whenever a raid member "fails." /EnsidiaFails to configure.

SRA

Incoming Heals

Modular and lightweight party/raid frames.

Show item durability and quality in the character frame.

TuiRaidTracker

Target Debuff monitor. Stacking aware, giving current and potential debuff status.

MiniPet, Always keep your little companion with you, based on the work of Carra.

A fancy LDB reputation display, show faction reputation and reputation change history

One large inventory.

Allows the user to preview and track their progress in the collection of various transmogrification appearance sets

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

Track all threat redirection ability transfers and cooldowns (Misdirection and Tricks of the Trade).

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