Membership sites can generate multiple stream of earnings once a base membership is established by selling affiliate products, cash from AdSense and other ad sales. Eventually the site can even be sold for a profit down the line like the topical sale of YouTube. There are tons of potential and the sky is actually the limit when it comes to the income generating potential of membership sites. Have you tried amember?
I have quite a bit of experience with membership sites. Your post is pretty vague though. What do you need to know?