Google Adsense is a free service but it also have some advantages

1. Your site needs to be approved by Google
2.There are restrictions on ad placement You have no control over the ad content
3. If a visitor clicks though and makes a sale you do not benefit
4. You only receive pennies per click
5.As a result a number of alternative products have been developed which provide these features:
6.The ads are for ClickBank products You earn full affiliate commission (rather than pay per click) for any sale
7.The keywords are either automatically determined from the page content or you can specify them yourself
8.You have full control over ad placement
9.You may have superior reporting stats than with AdSense