All cards with hardware encoding capabilities should work, but I'm not sure if there are any w/USB.
EDIT: Seems like there is a hybrid, though --> http://www.hauppauge.de/de/site/products/data_hvr1900.html
Probably expensive ...
EDIT: Seems like there is a hybrid, though --> http://www.hauppauge.de/de/site/products/data_hvr1900.html
Probably expensive ...