Ultima
Active, Cast, Spell, AEDD
Biggest AE nuke in game...
Level 40 Elementalist (Avatar Mage)
Level 40 Wizard

Unholy Portal
Active, Cast, Spell, Summon Pet
Summons forth a large demon to do thy bidding.
Level 31 Warlock (Avatar Sorcerer)

Unnerving Stare
Active, Cast, Spell, Utility
Should victim fail their saves vs paralisis, then victim will disengage from combat.
Level 7 Air, Level 9 Fire, Level 10 Water, Level 13 Earth, Elementalist (Avatar Mage)
Level 6 Warlock, Level 5 Wizard(Avatar Sorcerer)

Unspiritual Retribution
Active, Cast, Spell, DD
Damage spell which relies upon holy powers
Level 14 Priest (Avatar Cleric)