Google Adsense has started accepting sign up for its upcoming Cost Per Action (CPA) program, Google Referrals Beta. This Beta will allow you to select and display products and services Ads from Google AdWords advertisers database.

You will then be able to provide a few keywords to describe your website/blog and your website visitors interests after which ads will be displayed automatically based on keywords (similiar to how Adsense displays ads)

When your visitor clicks an advertisement and completes an action defined by the advertiser, such as a sale or sign-up, you will get paid. Earnings are usually high since advertisers pay more for leads than click throughs (which contains a debatable element of fraud)

Sign up here