Insanely Great has a posting with praise for eMusic, an online music subscription download service. Emusic doesn't have the top-of-the-charts stuff, but if you are interested in non-top-40 music, classical, jazz, etc., it's worth checking out. You can download MP3s, and you get to keep them after your subscription expires, so it might even be worth signing up for a short time, getting what you want, and then leaving.
I find it hard to browse online for music in general, and eMusic is no exception. Still, if you have a "wish list", they might find you several hits, at far less expensive than ITMS. I found a lot of stuff I had been meaning to get: Delerium, Thelonious Monk, Electronic, Señor Coconut, Sharon Shannon. (Yes, my tastes are wide.) And they have Vienna Teng's albums so how can you go wrong?
Please follow This link if you sign up so I can get a few more music credits — my wish-list is bigger than my current allotment! :-)