www.deepdiscountcd.com is probably the cheepest and has free shipping. www.cduniverse.com has more inventory but costs a little more. www.artist-shop.com has a wide variety and lots of progressive and fusion.
If you OK with used, I've found Amazon's used marketplace is a good source for CD's. Everything I've looked for has been available, including obscure titles. I find that DeepDiscountcd has good prices, but a limited selection.
You must have a verified phone number and physical address in order to post in the Audiogon Forums. Please return to Audiogon.com and complete this step. If you have any questions please contact Support.