As an alternative or extension to Google adsense you can show content links with advertisings on your site. Some words will trigger an ad related to the term. As you will discover on the Kontera Website it will double underline the text links on your website to make a difference between a normal link and a context link ad visual to your visitors! Kontera is not alone in this field but to my opinion definitely hot enough to mention here!

Kontera serves 5 different ad formats. Content Link Text, Text & Image, Billboard, Video and Flex as displayed below.

You can Join Kontera Free but they will approve your site so expect a few days before you can get the code and about a week to get the ads displayed on your site! This is a good thing for advertisers because it will make sure only pre approved quality sites can show their ads.