USB Vendor ID Confusion
http://support.atmel.com/bin/customer.exe?=&amp;action=viewKbEntry&amp;id=220

It seems if you are willing to work around their limitations and restrictions, perhaps you could just use theirs per above link.

I personally used microchip and their sublicense program for a small project of mine.  I couldn't find anything equivalent with Atmel, although it wouldn't hurt to ask.