This Stratfor analysis by George Friedman struck me as dispositive. It raises the possibility of every single kind of military attack on Iran - from air-strikes to attempt to degrade its nuclear capacity, to blockades, ground invasion, and bids to use military force to drive a wedge between the Persian population and the Islamo-fascist regime. Stratfor is hardly a peacenik outfit, and it concludes that almost all the options are extremely complicated and probably counter-productive. Here's the nuclear analysis:
First, the available evidence is that Iran is years away from achieving a deliverable nuclear weapon. Second, Iran might be more interested in trading its nuclear program for other political benefits -- specifically in Iraq. An attack against the country's nuclear facilities would make Tehran less motivated than before to change its behavior. Furthermore, even if its facilities were destroyed, Iran would retain its capabilities in Iraq, Lebanon and elsewhere in the world. Therefore, unless the United States believed there was an imminent threat of the creation of a deliverable nuclear system, the destruction of a long-term program would eliminate the long-term threat, but leave Iran's short-term capabilities intact. Barring imminent deployment, a stand-alone attack against Iran's nuclear capabilities makes little sense.
Friedman is not a great deal more optimistic about any other goal and the means to achieve it. I'm not a military expert, so I welcome any critiques of the piece. But it is pretty persuasive to me that we have very few effective military options against Iran, and the ramifications of an attack could be dire.