Sometimes, the simplest solutions are the most effective. As computer companies cater to the paranoid among us with such USB security devices as fingerprint readers and handwriting analyzers, this little upstart from ThinkGeek takes the most basic approach: plug the hole.
All you need to do before leaving your machine unattended is insert one of four "blockers" included with the gadget into your USB port, which prevent foreign flash drives or anything else from gaining access through that connection. The blockers can be removed only by the master key.
No complicated software or equipment to go haywire, though things could instantly go south if one of these got stuck the the port. In any event, it may not be the highest-tech security, but it ain't bad for $10 either.