I've got a few spell ideas.

Destruction: Rune of Oil Slick or Conjuration: Summon Oil Slick
Places a rune on the ground that explodes into an oil slick that slows enemies and can be set on fire!
Restoration: Better Ward
Wards can absorb physical damage and can be released deal to percentage of the damage absorbed and throw them back based on how much damage was absorbed.
Illusion: Mirror Image
The classic Mirror Image spell creates multiple copies of the caster to attract the blows and arrows of enemies.
Alteration: Transformation Deceptively Sweet Roll
Turns a single enemy into a sweet roll for 30sec. If cast unnoticed, a nearby enemy will attempt to eat the sweet roll causing it to be paralyzed and take damage over time for 10sec, (or be turned into another sweet roll)
Destruction: Better Wall of Frost
Summons a Wall of Frost for 10sec that will impede enemy movement until destroyed.