I don't have much experience with online advertising from a publishers perspective i.e. capitalising from injecting ads into your web content. As a web designer/developer I've always been engaged in creating sites for other people. most of which have had a specific function or market where serving third party advertising would not be appropriate.

As I've become more involved in publishing my own content, supporting it with revenue from something like Google Ads is enticing and hassle free. I know that making money from Google Ads isn't easy, so I'm encouraged to see more sophisticated 'open source' solutions available to smaller web publishers.

Take a look at OpenX, a free open source ad server that manages the selling and delivery of your online advertising inventory. At time of writing I only have the briefest knowledge of this product. When (if) I get the opportunity to test run this I'll offer more insight.