Amazon has recently announced their Context Links Beta program, very similar to the way Kontera displays their ads. According to their blog:
Context Links are for people looking for an easy way to generate money from the content they write. Bloggers, review sites, and people that have archived pages that are currently not monetized are excellent candidates for Context Links.
I have just placed the code onto some of my blogs but have yet to gauge their effectiveness. So far they have not appeared yet but a demo of how the links work can be seen here and here (dotted underlined links are Context Links). It certainly shows much promise!