A short history of nuclear-powered aircraft

Shaviv at DailyKos provides an interesting summary of the unhappy history of nuclear powered aircraft designs, featuring the Convair X-6, the XB-70 Valkyrie (very 70's looking, as you can see from the Wikimedia Commons image, but still a beautiful bit of technology), and the un-manned nuclear ramjet Project Pluto.

Is anyone currently thinking big and trying to make ambitious outside-the-box stuff like this?