Here is a quick, non-comprehensive list of advertising networks that publishers can use to generate website revenues. These are well respected networks that have a long history of on-time payment.
Google Adsense – Primarily a pay per click ad networks. Publisher revenues are earned mostly from clicks on contextually targeted text ads. There are an increasing number of graphic based ads, and there is the ability for an advertiser to pay on a CPM basis for specific properties.
ValueClick – A more traditional advertising network with a mixture of CPM and CPC based ads. The overwhelming majority of their ads are graphic in nature. ValueClick is prettygood about maintaining the quality of publishers in their network. Your sites should have several thousand pageviews per month to perform well on this network.
Casale Media – - Another traditional advertising network with a mixture of CPM and CPC based ads. Casale is very similar to ValueClick in the mixture of their ads and their publisher restrictions. I have found that CPM payouts are very similar as well.