According to a blog called Spudland, Mitt Romney has been photographed wearing a non-descript but functional Nixon "Private" watch.
|By Gage Skidmore [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons
President Obama has been seen wearing a Jorg-Gray 6500 watch that was given to him by his Secret Service detail.
This enlargement is grainy, but it's a simple black chronometer watch with subdials and a secret service logo.
If you'd like a Jorg-Gray 6500 watch just like the one worn by President Obama, you can get it right here: