In no particular order:
BBC Radio 3 (the cleanest internet stream I've ever heard), KPIG, KRSH FM - The Krush, Classical KCME (another extremely clean processed classical station stream), WFMU, WFUV, KTHN (country), WECK (oldies), KCSM (jazz), Radio Paradise, www.themellowsound.net, KROQ HD2 Rock of the 80's, Jazz FM 91, and many others.
Definitely going to check out some of the other suggested streams that are listed in this thread.