Earn Money Online

Google AdSense

AdSense is a contextual CPC (cost per click) network allows you to partner up with Google and display their advertiser's text and/or image ads on your website. When a visitor clicks your ads, you earn revenue.

What is AdSense?

Google.com earns most of its revenue by allowing other website owners to advertise on their search result pages. All this is managed through a program they call AdWords.
Now you can earn a share of the revenue that Google earns from AdWords by displaying these same text ads on your site.  In other words, you're helping Google advertise and they pay you a percentage (roughly 60%) of what they earn.
Every website owner should at least consider the program.  Even if your site is just for information purposes, you can still participate and make decent money with AdSense -- or at least enough to fund your website. So if you are one of those people that doesn't like the idea of paying for a site, this is an excellent way to earn your money back and then some.

Chitika

Chitika is another CPC network with a variety of ad types. One unique feature of Chitika is the ads only show up when people find your site via internal or external search.
Let's say someone finds one of your pages by searching for "blue hats" in Google. They will see Chitika ads related to blue hats. If another visitor just surfs on that same page by clicking through your site, they won't see any Chitika ads.
I tried Chitika on this site and the conversions were poor. This network seems to be best for shopping sites due to the kinds of ads in their database. Not many ads were relevant to my content.