One of the more common design approachs when it comes to HTML email designs is the jumbo sized photo. Often times this large graphic is placed inside of an overall email template containing the sites main navigation options. It could be argued that this extra stuff isn't nesecary, but it sure seems to make for an easy formula to work inside of. What is really fun to see is when the emails template is color coded to match the contents of the giant image.

Probably one of the biggest factors drawing designers to this style is the fact that it overcomes rendering issues in regards to making the email and text look the way you want it to. By embeding everything in the image the rendering variables are reduced. This often results in emails closly resembling print as an odd side effect.