I am very comfortable with display ads, which used to be called banner ads until the plethora of sizes made "banner" a little inaccurate. Starting with building animated GIFs, which are still used, and graduating to Flash, which I used to build many, many dynamic ads while at Teracent and Google. Compression was a big part of the build, and I took pride in my ability to compress to publishers' guidelines and at the same time, maintain a high quality image. Here is just a sampling of the banner ads that I managed to keep a record of.
DESIGN | HTML/CSS
Communication Arts Magazine