Cash always works well for me, as for things that you would expect people to already have, I could always use a spare laptop or 2 lol (I've already got 2). And things people would never buy for themselves is a great idea, but should have a cash option if the person isn't interested in a particular activity (ie sky diving or something else crazy like Yanik does - race car driving on the speedway), I'm a little too nervous about skydiving so it wouldn't interest me. Plus you have to take into consideration that some things may not be available to people due to where they live as well.
Someone's giving away their car right now and if the winner doesn't live in the U.S. they've offered a cash option.