Probably the first stop on trying to make money online. Really simple to use system to get ads on your site. The good thing about google adsense is that you can set it up and then just create your content.
Another way to get ads for your content. Install the code on your site and it finds keywords in your content and turns them into hyperlinks. Get the code installed and write your content just like google adsense. You can limit the number of links that you want to appear on your site.
Sign up with clickbank and you get access to promote all kinds of digital products. Ebooks are becoming the way to read information now.
If you are looking to promote more than just ebooks then you should checkout cj.com. Sign up and get access to all kinds of vendors and products. You have to apply to each program in order to get links.