So, here is a video at Fortune.com (yes, the magazine) that was originally made to promote a armed military robot. The guy that came up with this is partly funded by private investors with the goal of actually making and selling this to the US military. Supposedly there is a real prototype and the estimated cost is $30,000 USD. The prototype (not seen as this is a 3D 'show reel') reportedly mounts a weapon that blows holes through 1/2 inch steel doors.
Just in time for Christmas
Robot war machine