thanks for the sites,
they are interesting, although they are not exactly what i was looking for.
the site i saw was one that allowed people to write 'i want an xbox360', 'i want a sony XSDDFS344...' etc, and it would allow sellers to write what they have and it would match them. it wasn't specific to music/dvds, so only site left in your list is swaptree, but it was open and not in beta, and was more like ebay with the above mentioned differences.