I would recommend you flippa.com, NamePros.com and dnforum.com are the best place to sell domain. And, Before selling the domains try to know the value of your domains. It will useful for you to sell the domains at market for profitable price. There are many online sites are available to appraise the domain value. I had found one site called
TheWebPole.com here you can appraise your domain at free of cost.