I have had good results with facebook, but you really gotta find inovative ways to get your target market onto those groups.
1) Don't choose too small a niche as you will top out too early, unless you are making MFA type websites or have a very expensive affiliate offer working. 2) Build an email list. So often people just send their traffic away to these sites without properly warming them up, or capturing them for future sales. It's basic: find the need, fill the need, profit.
I have found article marketing to be very effective, especially if you can get your articles accepted at ezinearticles. They are owned by Google, and thus your articles appear higher in the SERP.