My picks are all the different MouseWorld stations, MouseHouse Radio 2 (#1 is too much like the DIS station -- just general Disney stuff, when I'd rather hear strictly park/resort stuff), and Park Hopper radio.
The MouseWorld stations tend to be my favorites, though, because there's such a variety of what I can listen to... the stations like MouseWorld X, X2, X3 play hour-long blocks of background music from areas like Frontierland, Adventureland, Innoventions, Main Street USA, etc.