Although I favor outright war with Iran to remove its insidious, poisonous influence in the world, the next best thing might be to heavily support such Iranian opposition groups as the Mujahedeed-e Khalq. This story by Daniel Pipes lays out a compelling argument for lending this group all the support necessary to make it a legitimate threat to the Iranian regime.
Note that I've always been torn in such instances. The US has admittedly supported groups and regimes, for expeditious and often unfortunately pramatic purposes, that have become future enemies. It's a long list, and mostly due to the Cold War, which is why my inherent distaste for such covert and often black ops is so conflicted. We had no choice in the Cold War, I believe, to fight the Soviet Union in anything other than proxy wars. A hot war with the USSR would likely have resulted in nuclear annihilation.
The same isn't true with Iran. Although I don't believe that such a war would be easily won, if the objectives were more clear than in Iraq it would certainly not be terribly difficult. But again, the point of this post: if we don't go to war against Iran, then we had better be supporting someone who will do the job for us. And I think Daniel Pipes has done a pretty decent job of telling us who that someone might be.