I would sell them on any site you can find. Not one site will work I think the best is to expand your exposure as much as you can. Even if you get only 1 extra view that is a potential. :)
We just opened up a forum section where you can list domain names for free. No fees, just list and you can sell it private without paying the extras that others pay. We only have one listing, but then again we only opened the forum today: http://killerdomains.com.au/forum/aftermarket