The humble banner ad. Over the course of my career, I've created a jillion of 'em.
Through the years of switching jobs and computers, not many of them remain in my hands. Still... here's a few good ones.
When designing a set of display ads, I find the best way to go about it (after convincing the Marketing Dept. to cut the copy by half) is to design for the most difficult size first. This usually means the wide-aspect ones, IMHO. Although the current Mobile 300x50s don't exactly give a designer a lot of space, either.
Fun fact: Sometime around 2006 (?) I was lucky enough to get a contract to design a series of banner ads for darwinawards.com, a fan favorite of offices all over the Bay Area during the Dotcom boom.
Created in Photoshop and Illustrator.