there appears to be a large blank spot under the list of internal sites. move the ad block from under "top downloads" to the left of it. an then move everything upwards so there isnt so much blank space -- that would be the first thing I do.
Your site looks well. You’ve placed only one ad unit, that’s fine, and the ad placement as well. Your ad title color & site link color should be the same. And you may change the link url color black rather than green. Use another big square ad unit in the body after the four segment of your content and blend it with your content.