Specificallt for Windows Media Player? Or you just want music that can be burnt using the program? If so:
www. albumbase.cxm
just change the x. Sign up =>check e-mail for registration => search for album or artist => click link, check if it's working (if not, try find another link) => go to site (rapidshare, megaupload, zshare etc.) => KA-CHING! your in business baby...
If you'll be doing a lot of downloading, it might be a good idea to get a premium account with rapidshare/megaupload, as most uploads are done to these sites, and without an account, they only let you download so much, like 2 times a month or something, I'm not sure...
Hope that helps!