iTunes Radio Stations

You may add any copatible stream to a playlist/Library - but you can't alter iTunes Radio list.

As Kay, says, any compatible station will play in iTunes. A compatible station is one using a standard MPEG audio stream as opposed to a proprietary format such as Real or Windows media. Once you play a station, it will appear in your Library, not in the default radio playlist which is actually a links page to a remote server. You can restart the stations from your Library. I have made a smart playlist for my radio stations using the condition "Kind is MPEG audio stream". Live365 is one source for tons of different radio stations that will all play in iTunes.