I'm somewhat with Josh on this one. Banners won't generate much revenue unless you are dealing with a private party or other very targeted ad system. The ad networks right now just don't work that well.
But what I do is have a "SOS" type area like Josh. Users can fill out a small form, be taken to a paypal page and make a donation. There are 3 levels of donations. Bronze, silver, and gold. Then, I let members who donate be allowed to create their own custom title. They really like that
Also, I use PhotoPost on my site, and every user gets 500KB to upload photos. Well, if you are a bronze, silver, or gold member, you get 5, 10, or 20 MB instead to store photos. So as you can see, that is a great incentive.
We also do other things like sell stickers and t-shirts occasionally, but the donations are easy to set up. So I think if you can find out what your users would be willing to pay for, meaning what features they would love to have and set up a similar scheme you could help make most of your money back
