Listing agencies are superfluous. Just put a note in the WhoIs record hinting that your domains are available for resale.
If you have access to your own web server you might consider using a landing page that indicates the domain is for sale.
There really isn't a "better place" to list domains. Pretty much every place where domains are routinely sold you will be selling to reseller marketplace, so unless it's a traffic domain (you've got stats) your price will tend to be quite modest compared to expected enduser prices.
Where to list, if you must: Afternic, Sedo, DNForum, NamePros - all the usual suspects.
You are far better off parking the domains using one of the parking services that allows you to implement a "Domain for Sale" link on the PPC lander. This will accomplish 3 things: 1) it will make you a few bucks if the domains have traffic; 2) it will build a traffic record; and, 3) it will expose the domain's "for sale" status.