Firebomb: great spammable group killer. Three targets hit initially, plus the aoe effect from Firebomb on each bounce.
Spirit Barrage: powerful single-target cast, also refunds a bit of health each time.
GoTD: aoe snare, slow down those ambushes.
Haunt: nice periodic dmg effect to wear down those tougher mobs/bosses.
Horrify: panic button that also gives you a nice bit of mana in return.
Firebats: really good for finishing off groups, and even for bosses. Insane dmg!