Napster to Go
For $14.95 a month you can get Napster to Go. They have a full list of compatible players, but it works with most players that are Play for Sure compatible.
There are a lot of things I like about Napster. If you simply want to stream music you can run it from a web interface. Unlike Yahoo it's not reliant on IE, so you can use Firefox or another browser if you like. It is very quick and very stable. I've had some problems with Yahoo being a bit unstable, but not Napster. The files download onto the player quite a bit quicker than Yahoo. They have an extensive catalog of music and so you can find almost anything you are looking for.
I think those are a lot of positives and certainly overshadow the negatives. You cannot rate music. This is something about Yahoo and Rhapsody that I really like. The search interface leaves a bit to be desired. It seems you have to make quite a few clicks to get to what you want which can be a bit annoying. Other than that there is really nothing wrong with the service that I can tell. It's a bit expensive, but still $15 a month is equal to a CD a month.
My parents love music, but aren't the most computer savvy people. I picked Napster as the product to give them for Christmas along with a compatible player. Mom loves the player and finds it quite easy to download music. Dad loves to create playlists for when he's working mixing everything from classical to The Lettermen. I don't think it's the best product available, but I find it very easy to use and I find it to be very robust.