http://www.ebay.com/itm/Mini-Pro-Micro-ATmega32U4-5V-16MHz-Replace-ATmega328-Arduino-Pro-/191756162028?hash=item2ca58ed3ec:g:eWYAAOSwnH1WZ8IF
1cm shorter than the Nano. a bit more "ready-to-run" than the Pro Mini
the 5v version is 16mhz