WowAce

Displays the locations of the chests for the Treasure, Treasure Everywhere achievement

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

Wowhead Data dump for GatherMate

Angry Assignments

CraftList2

Track of your tradeskills across characters, create small buttons for them and track cooldowns.

MendWatch

FuBar_TransporterFu

HUD that you can tweak the way you want.

Some handy events that should exist in the default UI

Automated smart raid marking to speed up trash clearing in instance runs

Configure triggers to send messages to your raid team such as timers, rotations, and health/power based triggers. Raid smarter not harder.

ItemBonusLib

QuestLog

manipulate the minimap in numerous ways; move, scale, skin.

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

Compact rune and proc display for Death Knights.

Raid loot tracking and text generation

ImprovedRWF

LCDs for WoW