To sell domains you own:
sedo.com, afternic.com, namepros.com, dnforum.com, domainstate.com, ebay.com, adultindustryauctions.com
Afternic.com also has a Bazaar "reverse auction" system for faster sales, although it tends to be a wholesaler marketplace.
You can also selll them here. Or list them on every available venue for maximum exposure.
