Pandora and Slacker. Depends on my mood. I've had my Pandora account for a few years so the stations are pretty close to perfect for me. My Slacker is getting there.
Posted from my CrackBerry at wapforums.crackberry.com
Now that Slacker Radio has been released in Canada I have primarily been using it. I also have Nobex and FlyCast. A Pandora release up here would be awesome as well!