Well here are some suggestions sorted by sphere:
Fire: Fireball / Incinerate
Air: Lightning bolt / Wrathful skies
Water: Falling frost / Frozen heart
Earth: Blade wind / Petrify
Nature: Sleep / Breath of the Dragon
Astral: Mind burn / Soul slay
Death: Shadow bolt / Decay
Blood: Summon Imps / Agony
These are just some examples - what you need to take into consideration is what kind of magic is available to your mages/pretender and is there some synenergi with respect to research. E.g. frozen heart and quickness both come from the alteration school of magic.
I hope that helped - I remember how vast the spell options seemed when I started to play
