I ain't a big fan of Apple, but I have grown to love Itunes. It is capable of keeping its own copy of your music, and the Genius function is brilliant. You don't have to use Itunes store to buy or download music.

Currently I'm over 4000 tracks on my Itunes, and the ability to select one and have Genius either suggest other music I might like, or to look at my library and select, from that 1 track, a playlist of 100 similar ones is brilliant.