Check out the Ultimate Footer Ad
This tool was so awesome I had to buy it. It acts as an ad rotation tool, a split test tool, as well as a great way to boost opt ins to your newsletter. In the past I had told you about Instant Slide Up footer ad, but Ultimate Footer Ad is so much better AND it's $20 bucks less (only $47) and you get lifetime updates, you can use it on as many domains as you want. It's a no brainer. Check out the videos at their site. Ultimate Footer Ad
Best of all it has a 365 day money back guarantee, and lifetime upgrades.
To install it you need to know how to add a SQL database (to track stats). I had mine up and running in about 5- 10 minutes.
You can even make your own graphics and use those if you want. It's just very cool. Check it out
If you want to see it in action, I'm using it at www.schoolofpodcasting.com