You can also see "per-page" stats for your ads using the AdSense Tracker tool:

For each page you can see the number of page views, clicks, and CTR (click-through rate). This is probably the most powerful feature of the AdSense Tracker. Whereas you can only create 20 channels with the Google AdSense reporting, the AdSense Tracker gives stats for every single individual page that has the tracking code. Pages are ranked according to the number of clicks, so you can quickly see which pages are resulting in the most clickthroughs.