Recommendations for solid aftermarket domain sites

[Stouch]

You could try sedo.co.uk for domains for sale, dnforum.com & domainstate.com for boards with sellers & sale sections, however you really need to weed out the dross as in all sites like these.

If you have a domain in mind I would approach via the whois details. A word of warning though, lately mass produced "I want to buy your domain" type emails are hitting inboxes all over the place and a lot of the bigger sellers I know arent even responding unless its very obvious that its from someone who appears very serious.