I like the Nightwish station, although I think my favorite single-artist station would be the Pelican one. Pelican is an instrumental post-rock band, so with that station, you get a lot of really intricate and interesting instrumental tracks, most of them being some form of rock. It's a great station to do homework to. There's a coffeeshop I go to a lot that uses Pandora for its music, and the baristas who are working get to chose with station gets played. One of them found a station called Hip Hop BBQ that plays a lot of great nostalgic rap tracks. It's always fun to be in there when they're playing it.
Close call between Chumbawamba and Bloodhound Gang. I also listen to "I'll Make a Man out of You" frequently.
I have two stations that I switch between on a regular basis. Kelly Clarkson for when I need my Top 40 fix and the Offspring when I work out.