WowAce

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

Keeps track of quests.

Shows you a much bigger icon selection frame

UnitActionBars

Barks at you when you target a crowd-controlled unit

Shows ZoneInfo on the World Map in a perfectly cromulent fashion.

Keeps track of your top hits, heals, criticals, etc.

FuBar_HonorFu

Show what quests have changed

Reduces interface tedium by doing the little things for you.

Alternate Power- and Combopoint/SoulShard/HolyPower-bar

View bank, inventory, mail, equipped and guild bank contents from any character anywhere!

Display auras on action buttons.

Raid Frames using the oUF framework.

OneBank3 will combine all the bank bags into one frame.

PT3Browser

A replacement tradeskill window

Does stuff for sachmo

Kaliban's Class Loot List Star Display

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