Not so much clean-up crew as AOE blasters. I've gotten some good use out of waterball*, cone of cold, and chain lightning against groups of lesser foes. These have often been able to put out some nasty damage collectively, and either taking them out right away or softening them up so the martials can take them out in one hit instead of four helps a lot. So my tactics often boil down to: use big AOE vs many targets, or use slow or fear against single strong targets. The latter is useful, but generally not super-exciting.
* Elemental sorcerer with water element, gets fireball with water dealing bludgeoning damage as a bloodline spell.