there’s walmart, itunes, raspody… etc etc…i hear realplayer offers a nice crack software that allows their music to play on an ipod 
mp3.com has a list of all the sites available along with their respective price, encoder and bitrate
the only beef i have with wma’s is the difficulty in saving licenses. if you format your computer, the license can’t seem to restore properly; even after they were back-ed up prior to the format. aac’s atleast can be reissued to your computer