I'd like to see a Charm spell where you actually 'take over' the person or creature you charm. That would be wicked. So if you're a necromancer you can actually become one of your zombies and pay a visit to a town!! Or take over an attractive female and seduce a guard to let you in to a locked room etc

Even more interesting if a drool worthy 1-4 player co op was implemented (I can dream...but not a mmo..that would be cack!)

The charm spell effect you mention could be interesting. The modding posibilities opened by the chance of change the control to NPCs would be priceless.