WowAce

Uses guild notes to add alts' main names to chat windows and other places

Bidder for DKP points. Usable as standalone bidder, or with DKP - Manager to manage points.

Provides information of tradeskill and crafting materials that are in the banks and bags of your characters.

Doodle

Enables the filtering of items when you visit a vendor

DotDotDot

A customizable casting bar replacement for TBC Classic & Classic WoW

Improved Quest Tracker

FuBar_CRDelayFu

RaidSpy

Simple right click casting.

Mapster's Minimap brother

Set the clicking action for Grid buttons

AltClick an item in your bag to add it a mail, auction, or trade frame, and alt-click to buy a stack if reagents.

Rep2 displays a message, which shows how much reputation you gained, and how much is needed until the next standing.

QR Code builder library

Show extra information about Jewels and Enchants in tooltips.

Embeddable chat throttling library with traffic shaping and priorities

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

Monitor the remaining duration on your Mysterious Eggs and other perishable items.