WowAce

Tracking and ranking of dps/hps in a guild.

Shows your standings with the factions.

A small checklist for raid (de)buffs and who brings what.

Acolyte2

Adds party/raid role icons in useful places

Simple right click casting.

Gathers statistics on certain chance-on-use spells, also known as procs.

SysMon plugin for any DataBroker display.

NabuFiveSec

Doublerightclick casting, autolure and sound enhancing

FuBar_PoisonReminderFu

This will keep track of how much you have paid per item in your inventory. Only one of (Auctionator, Auctioneer, AuctionLite,...

Displays friend notes in unit tooltips, at logon, and in /who results.

Filters AFK and DND messages after you've seen them once.

mHud

TrackingBar

MainAssist

FuBar_RaidBuffFu

Estimated time until current target will die.

LCDs for WoW