For those who are interesting in including a _lot_ more banners on their sites, i have found that adpeeps is a fantastic little script. adpeeps.com. (I
am in no way affiliated to them by the way).
The script generates a script that you can put on your site, where you want banners placed, unlimited amounts of banner scripts/positions.
But the beauty of this script is that it can do geotargeting, so you can show different adverts to visitors from different countries, just like adsense can. Plus you can put text link ads into it and it will output code that looks like adsense. Unlimited definable banner ad sizes too. I also chuck my adsense ad codes and adsense referrals codes into the rotator too.
Really, I cannot speak highly enough about it. Not too cheap for the beginner but well worth it for CTR optimisation on larger sites.