The one I'm listening to right now is http://theRADIO.com
Many jazz channels, including "The Jazz Cave," which is on right now.
Others included: http://music.aol.com/radioguide/jazz-radio
www.slacker.com (appears to have good jazz selection)
Live 365 http://www.live365.com/index.live
http://www.181.fm// (classical jazz)
"Try KCSM They play jazz, but I'm not
sure that they don't play other stuff too."
http://www.sky.fm/smoothjazz/ (other jazz types as well)