Most of the entries in our recent "Harder Than Granite" contest would be a good fit for this. Apples to Apples, or would also be a possibilty. (though the former costs money)
Basic exercises from a writing class might work as well. I'm always fond of the one where you name a few esoteric cars (ie an immaculate orange Plymouth roadrunner and a powder blue UAZ jeep with run-flat tires) and challenge the people to describe the owner's home just based on their vehicle.
Games of imagination are never truly done. Yet tomorrow we shall start another one.