USB Firewall
USB firewalls that block certain device classes do not (yet) exist.
Um... actually, they do. There is a McAfee product, Data Loss Prevention that has just that sort of functionality built in. Alas, it is only for Windows devices, but there are likely similar products out there. It is a pain to administer - it has all the hallmarks of an acquired product that was slapped into an existing management console - and is likely to be resented by users as it will keep them from doing what they desperately want to do (infesting the corporate network with malware), but it exists.