WowAce

Heads Up Display with Player and Target Info

Fires events whenever a raid member "fails."

Kiwi Plates

Deathknight Rune Display

FuBar_VampwatchFu

Compact rune and proc display for Death Knights.

Aura alarm.

Entertaining kill-shot notification.

Target Debuff monitor. Stacking aware, giving current and potential debuff status.

Tracks the Blood Shield for Death Knights.

Compact & customizable filtering, monitoring and grouping of buffs and debuffs

A sexy logarithmic cooldown bar

CombatLog in SimpleCombatlog style

Sheppard

Tracks, transmits and displays the cooldowns of your raid.

Provides quick access to information on your group and their equipment, enchant and gem choices.

Desesperated announcing to clearly show the skillings of act inplay.

Displays the time remaining before your (temporary) pet is dismissed.

Broken in Midnight. I recommend MidnightFocusInterrupt instead.

Mutt (Macro Update Target Tool) provides slash-commands that can patch the predefined targets in your macros.