This is a great subject in my humble opinion! I listen to internet radio every day. Here are my fav's - some have already been mentioned:
WBGO - Newark - THE jazz station in NYC - great mainstream jazz!
KPLU - Tocoma - a good station for soul jazz, mainstream jazz, a little bluesy jazz..
WBEZ - Chicago - good jazz, latin and blues - specially "Blues Before Sunrise"
WCPN - Clevelend - good jazz programming too...
WWOZ - NOLA - great New Orleans jazz and R&B plus some rather out jazz...
KFAI - Twin Cities - Communty Radio - great 50's R&B programming
KCSM - my Uncle Bud is on Sunday Nights - need I say more?
WLNZ - Lansing - good swing and mainstream
I also listen to WEMU which is a great local station and when in the area, WCMU, WBLV and WCPN amd sometimes WGVU.
I guess I'm a bit of a junkie!
Best,
RJ