A recent episode of "The Universe" on The History Channel, entitled "Space Wars," featured a rocket-boosted rod of metal (able to withstand the heat of reentry into the earth's atmosphere) that could be launched from space at a ground target. It's high speed (probably 5 or 6 thousand miles per hour) at impact could generate enough kinetic energy to penetrate deep into an underground facility and completely destroy it.

Coincidentally, the U.S. military has recently contracted with McDonnell Douglas Corporation to integrate a Massive Ordnance Penetrator capability with a B-2 (stealth) bomber. See "Is the U.S. Preparing to Bomb Iran?" The MOP is "a 30,000-pound bomb designed to hit targets buried 200 feet below ground." That certainly would provide President Obama with an option if negotiations with Iran fail.