The Hughes XF-11 http://en.wikipedia.org/wiki/Hughes_XF-11
The Beechcraft XA-38 Grizzly http://en.wikipedia.org/wiki/XA-38
The Bell XP-52 http://en.wikipedia.org/wiki/XP-52
The Boeing XB-15 (with better engines of course) http://en.wikipedia.org/wiki/XB-15
I would have loved to have seen the Grizzly in action
The Beechcraft XA-38 Grizzly http://en.wikipedia.org/wiki/XA-38
The Bell XP-52 http://en.wikipedia.org/wiki/XP-52
The Boeing XB-15 (with better engines of course) http://en.wikipedia.org/wiki/XB-15
I would have loved to have seen the Grizzly in action