Non-combat spellcasting as a way to resolve quest challenges.
Examples (apologies for AD&D references):
Knock, Levitate, Fly, Disarm Trap, Detect Trap, Detect (various), that sort of thing. I know Companions can serve many of these functions, but I think it would be fun for the various casters to be able to do something other than Heal, Summon, Protect, Blast, and Debuff.
As I said, non-combat casting.