I'm currently experimenting with advertising systems, and want to invite you to try an idea I had. I run a free hosting site, so in return for this service our clients put ads on their sites. I currently host almost 1000 active sites (this is not including sites that aren't built) as well as ads on my site. Your banner will be run on some of them based on the keywords you provide.
Since this is a new system, you get 100 free credits to try it out. If you like it, you can buy more and only pay for results. Check it out here: http://ads.ismywebsite.com/
Be sure to let me know your opinion. (And no, I don't have any objections to hosting sites running there.)