So you wanna make some cash from your website

Then check out a few of the ad services that pay you when a user clicks.

AdSense (Google):
http://google.com/adsense/

Publisher Network (Yahoo!):
http://publisher.yahoo.com/

ValueClick Media:
http://www.valueclickmedia.com/index.shtml

Casale Media:
http://casalemedia.com/

ContentAds (Microsoft):
not available yet