How to generate website revenue

Ok, as a freelancer I'm baffled on how you can create sites to generate revenue, specifically for freelancers. I mean, when I think of revenue I think of a shopping cart in an e-commerce site, but I'm not a retailer--I'm a web designer.

How can a freelancer generate revenue? The closing thing to mind to me would be through click-by-click advertising, such as the banner advert ust on top of talkfreelance. How else do you guys bring in the money, as much as I like freelancing I think financial stability is also important, because if you want to be the best you have to feel free to be your best. I think hopping from client to client without anything in between is kinda scary.

So how do you bridge the gap? My portfolio is a portfolio not a shopping cart. How do you do it? Forums? How can a forum even make money without a membership fee?

Wow I'm amazed how many ?'s I used. ^.^