Pay Per Click Contextual Ad Networks | Earn Money $250

These are networks like Google Adsense that have ads displayed based on the content of your site. Typically you will get paid per click from these types of contextual networks. Here are a few (there are likely many many more):

1. Google Adsense

2. Media.net (now manages both the Yahoo and Bing ad Networks)

3. Infolinks

4. Kontera

5. Vibrant Media

6. GumGum (In-image ads)

7. Chitika

8. Clicksor.com (both eCPM and pay per click).