DP = Forums.digitalpoint .com, Its a Forum, not recommended because of High risk of fraud..
V7N.com - you can sell your domain in forums.v7n .com but very low chances(time wasting...) Google Search Result
for selling your domain
Also you can sell your domain in namecheap.com(if you've domain in namecheap)
Free Service: http://www.websiteacquire
.com - my favorite