Find the most powerful magnet you have. Ours happens to be the magnet "key" that keeps our toddler out of the cabinets. Gently slide the magnet around on the wall, near where you'd like to hang your whatever. The magnet will snap on to the closest drywall screw head it can find. Pow, there's your stud.

Edit: Do not drill exactly where the magnet stopped. There's already a screw there.