Automated playlists using similar artists.

[JoyMonkey]

I've been listening to Real Rhapsody at work for the last few months and I really like it's "Artist Radio" feature, which plays your selected artist along with loads of similar tracks. It works really well, probably 1 in 10 songs played are by your selected artist and the rest are very well chosen similar ones. I don't know where Rhapsody gets it's 'similar artist' information, but it's spot on. It's a great way of finding new music and rediscovering old stuff.

I'd love to be able to generate playlists for my iPod like this (I'm sure it would be very useful for home jukeboxes too). Are there anything utilities out there that will do something like this?
Any kind of playlist will do, converting it to an iTunes playlist doesn't seem to be too difficult.

I've searched around but can't find anything and I'm not sure where to ask this. Anyone?