I am probably a little slow on the uptake, but I recently discovered Pandora.com – a great online “radio”. You select some of your favorite artists, and Pandora plays music along that same musical vein. You can rate the music a thumbs up or down, and Pandora will tweak your musical selections for you based on your preferences… all for free! No downloading!
And it works on the iphone. Click here for Pandora.