Here are the most effective places to put ads on your site.
1. On the exteme left, just below the navigation bar
2. Just below the navigation bar
3. Top of the content section (Hottest area)
4. Left of the content section
5. Just above the footer
Here is an image provided by google for adsense map.
Google has also has published a list of the highest performing ad sizes:
336×280 large rectangle
300×250 inline rectangle
160×600 wide skyscraper
Tags: adsense placement, google money making, optimal adsense placement, where to place adsense