I have accidentaly run across another website which I believe is not listed here, but which I also consider to be good:

http://www.usbmadesimple.co.uk/ums_1.htm

The guy who made it is actually quite good, his advice on the Microchip forum proved really useful and this is how I eventually stumbled across his webpage about USB.

Hopefully it is no already listed in the article, I have checked, but I might have missed it.

Regards,
Cristian