I like the 728x90 banners, the 120x600 vertical banners. I've seen them even wider like 980x120 and those look great at the top of a blog or custom gallery, as a header.
This might be worth looking at for good standard sizes. The medium rectangle is often selected as one of the more popular for good CTR.
https://www.google.com/adsense/stati...AdFormats.html