I have seen a few sites that had multiple adsense ads, and thought that was against their terms, but looks like they allow it now.
From their email
From their email
Since you are allowed three, I reckon two little one unit ads on either side of the quick reply box might be effective. Figuring out how to implement that would be another thing.Multiple ad units [font=Arial, Helvetica, sans-serif]To provide even more value to your users, and to help you further monetize your web pages, we're allowing publishers to place up to three ad units on every web page. Our system will automatically recognize the additional ad units, and will serve unique ads to each. Your ad units can each have different color palettes, formats, and alternate ad URLs, providing you with the flexibility you need to incorporate Google ads into your site design.[/font]