Granted, it's not as useful as the USB missile launcher, but this 150x microscope could come in handy around the office. It's currently available only in Japan, so you may have to content yourself with the missile launcher for now.
Link
Previously on Neatorama: The 10 Weirdest USB-Powered Devices
They're fun to play with, but get boring relatively quickly (although my 5 year old got one for her birthday in February and still brings stuff in from outside to look at).
http://www.aldi.com.au/au/html/offers/2827_9426.htm