We have XM in both our vehicles, and the subscription gives access to all XM's channels via stream on our PC. It's pretty handy, especially when I arrive home right in the middle of a good program on XM, I don't have to sit in my car to hear the rest of it.
I already listen to a few stations on the internet, syndicated programs that aren't picked up around here can usually be found online(Dr. Demento, Rockline, Ron & Fez). Most radio stations have live streams available, so if you know which station carries which show, you never have to miss out.