LALA
it is not quite a store but
lala.com (still in beta) may soon become one of the best places to freshen-up your CD collection. As discussed in
another thread you get an invitation from a member (I have 9 left if anyone wants one). You list the CDs in your collection and those that you want from other members. As soon as you get the envelopes lala sends you when you register you can start trading. You pay $1.49 per CD you receive. Their catalogue is very good: I could find a couple of my CDs which are not listed on amazon. As for the actual availability of CDs, it's too early to say, but I have traded 7 CDs in my first week (sent four and received three).