Here’s a tips article from Google pointing out the best places for ads in a page.

Of course it’s particularly relevant for those of you that run ads on your pages, and you -probably- already know these, but I’m posting it for another reason.

It gives a good idea of where the visitor focuses on a page, or where not, which you can use to decide where you place your page elements when designing those split testing versions/variations of your pages.

https://www.google.com/support/adsense/bin/answer.py?answer=17954