We had a clothes swap party - everyone had to turn up in fancy dress of their choosing, then when people arrived they got given a number on a kiddies plaster (you know, mickey mouse, etc etc playing on the plaster) to stick on their forehead.
Then every 45mins or so the cooker timer would go off and the host read out a list of numbers as pairs. Everyone had to find the person they were paired with and swap costumes.
My friends gf put a lot of effort in, so that people wouldn't mismatch size-wise ridiculously. I think I started as a vampire, turned into a cheerleader (!), then an american football player and a slutty nurse at the end.
Was brilliant fun, but needs an organised mind (and close friends) to pull it off.