high end usb sound card recommendations for linux?

[Johannes Wiedersich <johannes@physik.blm.tu-muenchen.de>]

The input quality of my laptop's sound card is rather bad. I'm thinking 
of buying a high quality sound card for my laptop in order to upgrade my 
sound experience on using the laptop with my hifi set.

Requirements:
- high quality audio input and output (preferably better audio quality 
than mp3)
- supported by debian etch/sid
- usb or firewire or pcmcia; (usb prefered)
- stereo in- and output (surround sound not required or used)

any suggestions and/or links to linux tests are highly appreciated!

Thanks,
Johannes