Credits to jacen for the last update: http://gamebanana.com/tf2/guis/26400
This mod replaces the new menu backgrounds with the original menu backgrounds from older days of TF2. Three backgrounds cycle. The first background, Spy/Heavy/Demo, will show until the MvM update's background stops being the only one shown (TF2's orders, not mine). This mod also removes the character images.
Works for both standard/widescreen.