It's good to list your domains on the big marketplaces, but don't expect much because unless they are truely exceptional they will just be lost in the crowd of 100,000's of other names.
The best thing you can do to let people know your domain is for sale is to use a parking page that says so on it. Most of the big parking companies have this feature, as do Sedo and Afternic.
Listing on the major domain forums is beneficial too, but expect to sell for reseller prices. Ebay is also good if you want a quick sale at a lower price range.