Bitcoin is really ideal for Internet advertising, no banking fees, no giant list of rules like Google Adsense, and for most people that will also mean no taxes, money earned can be reinvested in web hosting or other services without leaving the Bitcoin economy.
These are the ad-networks that I know of:
This is the statistics for BitcoinAdvertiser (BA): stats. With BitcoinAdvertisers, the impression count has be reset several times so the stats are not correct and not very useful. Also this site had more BA ads but still AA pays more, and obviously from the stats a lots of clicks are not counted by BA, I am not even sure BA pays. I have therefore discarded BA, and put only AA ads on the website.
If you know more networks, please post them in the comments.