I decided to sign up for Google AdSense and start serving content specific ads (in this case basketball specific) on my InfiniteHoops.com pickup basketball site. The Google team first reviewed the site and suggested that I push more content outside of my login before they would agree to serve ads. Having more functionality for unauth'd users is feedback I had received earlier from members of this community in fact. Anyhow, after making some site reorganization and additional functionality, I resubmitted the URL and they reviewed and agreed to serve ads.
I decided on Google ads as they are the least intrusive. No images, no flash, no popup garbage. Just simple text that might appeal to my users. Anyhow, one gets to choose the size and colors of the ad banners and then it's a simple matter of pasting their markup into your site. I put their markup into a User Control so that I could include a simple tag on multiple pages.
So now it is business as usual. Find ways to grow my user base on a limited budget, i.e., zip.