Metal Storm.
http://www.youtube.com/watch?v=d8hlj4EbdsEIt's still in the prototype process, but it's expected to revolutionize weaponry to the point where a 36 barrel version can fire a million rounds a minute. That calculates to 462 rounds a second per barrel.
Since the test subjects have 36 barrels, the result would be that organic soft tissue would be completely shredded into a bloody fine grain splattered across a side walk.
I personally am waiting for the grenade adaptions. When adapted to a plane, carpet bombing would never be the same.