The only suggestion I have is to stick to standard banner ad sizes. The banners I made back in 2003, while good, didn't get the wide adoption they could've because they were non-standard sizes. If a site owner can't fit a banner in their current layout, they won't use it.
Here are some guidelines to follow:
http://www.iab.net/iab_products_and_industry_services/1421/1443/1452