You can try to sell directly to site owners. You can try www.associatedcontent.com, but you'll never get more than a few bucks. I'd say try to sell to a site first. If you can get them to agree to nonexclusive rights, good for you, and you can make a bit extra with AC or other private sales.
Post in the DP content forum offering your services. You could also try signing up with Constant Content, and Article Warehouse who will sell articles on your behalf.