Aten CS22U 2-Port USB VGA Cable KVM Switch w/Remote Port Selector
 
Use one monitor and a USB keyboard and USB mouse to control two different computers by switching between the two.

(from Aten product description: )
  •  One USB console controls two USB computers
  •  Supports multifunction mice
  •  Multiplatform support - Windows, Mac, Linux and Sun
  •  The console USB ports can be used for USB peripheral sharing
  •  Superior video quality - up to 2048 x 1536; DDC2B
  •  Bus-Powered