Hello. Can't really help much here (no personal experiences in selling things online), but:
if you have a price in mind for your items I'd suggest to go with sites that don't require a "fee" to post announces
if you plan to sell "collectables" releases with a decent market value, then I'd go for an "auction like" thing.
But if you send me a list of the things you want to sell (cds) I could help you in other ways
. ha ha.