WowAce

A library to provide a markup syntax

Babble-2.2

A library to help with localization of factions.

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

A library to provide information about zones and instances.

A library to help with localization of in-game subzone names.

Additional information about player spells.

Does stuff for sachmo

Database of Diminishing return categories and general data

A library to provide a clean dropdown menu interface.

A library to help with localization of Zones.

Various libraries based on LCD4Linux, offering users lower-level UI customizations.

A library to help with localization of item types and subtypes.

TabletLib

A library to track nameplates.

Some handy events that should exist in the default UI

Talismonger-3.0

ItemBonusLib

IncomingHealsLib

A library for PvP and Battlegrounds