Most interesting one I've heard is a clip that one of my former coworkers took from Finding Nemo. It was a few seconds of the seagulls going, "Mine, mine mineminemineminemine..."
I also have one assigned to another coworker that's a horse whinny. Guess why.
Other than those, which are for fun, I've either got it on a regular, boring ringer, or it's on vibrate. I hate hearing cell phones go off in public places, too, especially when the user pauses a few seconds to read the caller ID and decide whether to answer or not.