Griffin iMic
$35
Works under Linux
Telex
Their webpage stinks--it provides very little details on their products
Griffin Technology PowerWave
$99
Onkyo SE-U33HUB/MSE-U33HB
MSE-U33HB $50
Onkyo SE-U55
$100
Onkyo SE-U33/MSE-U33
Same as MSE-U33HB, but the U33HB doubles as a USB hub and this one doesn't
Onkyo SE-U55X
Onkyo UE-155
Only available in Japan?
Audiotrak OPTOPlay
output only $70
Audiotrak Maya 5.1
$100
Stereo-Link 1200
They advertise Linux compatibility
$150
Egosys U24
Buy it
Egosys U2a
$200+
Edirol/Roland
Soundtechnology ST190
Can't find price info
USB One
Can't find price info
Apogee Mini-Me
high-end
Yamaha UW500
$300
Digidesign Mbox
high-end
I-O Data D2VOX
Opcode SONICPort
$250
BKM NP-350
Only input is a monaural microphone jack Can't find a retailer on the web

Yamaha Cavit

Other sites:

USB audio for linux
USB audio with linux
USB audio on linux
Linux:
http://www.alsa-project.org/alsa-doc/doc-php/template.php3?company=USB&card=Generic&chip=Generic&module=usb-audio
http://www.linux-usb.org/USB-guide/x319.html
USB audio specification
http://www.usb.org/developers/devclass_docs
Linux Compatibility list for USB audio devices

http://www.usb-audio.com/