http://www.guardian.co.uk/internatio...392687,00.html
The invasion of Afghanistan and Iraq has placed US forces on both sides of Iran. Iran also has a long coast adjacent to the Persian Gulf and the Gulf of Oman.
Iran spends $4.3 billion USD per year on their military, only slightly less than North Korea. However, NK's GDP/capita at PPP is about 1,000$/year, while Iran is 7,000$/year. It has a half-trillion dollar economy and 70 million people in it, as opposed to NK's 30 billion dollar economy and 23 million people.
In many ways, Iran is the strongest of the Arab states. Their economy is twice that of Saudi Arabia's or Egypt's, and only Egypt has more people than Iran (and then only barely).
They are a pissant of a nation next to the USA. But, I don't know of a stronger nation that the USA has taken on in a direct military conflict since WW2.
Oh, and as an aside, I
heard Iran has a bunch of carrier-killing cruise missiles apparently. No idea how reliable this data is.