Forums are great opportunity for marketing. From forum content you can see what people are looking for.
If I want to get referrals for a getpaid program, I will go on
http://Globaltalkforum .
Selling domains, web-hosting packages.. are possible on many "website discussing" forums, including this one.
It is a good feeling when you can offer a service or product to someone, for whom you know in advance that he's interested in it.