I took a look at the banner image sizes posted in the banner forum and they're all over the place when it comes to sizes. I took one that was posted recently and used it as a template.
Here's a couple I came up with. Anybody else want to make some too?
These are 150x1200, which is the size posted in the banners forum, but they look smaller when opened in this forum. Also, you have to open them up to see them as banners.