I see four ways in which Israel could attack Iran.
1. The first has already been alluded to in other posts, and that is by air. The exact route that the Israelis would use is the big question, but in the past, they have been very good at playing chicken with many different countries' air defence systems by flying right along the border, thus ensuring that they did not, in fact, violate anyone's airspace. That is how they managed to pull off the raid on Entebbe back in the 70's. If they wanted to do the same thing, they would fly south over the gulf of Aqaba, hang a left at the Jordan/Saudi border and follow it until it becomes the Iraq/Saudi border. At this point, the choices become numerous. Knowing very well that the Iraqi Air defense system is non-existant at the moment, turning north-east over Iraq and popping over the Iranian border would be very easy. Or, they could continue to follow the border until it reaches the Persian Gulf, cross the Gulf wherever they like and hit Iran almost everywhere. The problem with either of these routes becomes refueling. Air to air refueling would be mandatory, and that would be the sticky part. Personally, I would put the tanker over Iraq and the hell with the consequences, but that could be problematic, particularly for the US. As for the poster who said that the Jordanian and Saudi Air Defense systems are clueless, think again. Jordan's is weak, true, but furthermore, they have no interest in provoking a battle with Israel. They would lose. Saudi Arabia has AWACS, F-15s and IIRC, F-16s, so their AD systems are quite good. It is their reaction that might be difficult to predict, but they would not be enamored of a nuclear armed Tehran. I could easily imagine them saying, "Oops!! Sorry! We were asleep. We never saw anything!"
The other route would be the northern one, heading along the Turkey/Syria border. This would be far more dangerous, but possibly doable... once. After that, all bets are off. A third possibility would be to get Ankara to allow Israeli overflights, and I believe that Ankara would probably allow them given that Iran is not exactly the country that Turkey would want to see as the regional nuclear power.
2. Land Forces: I do not ever see this one happening, but after thinking about Entebbe, I figured hey, why not. Israel has considerable heavy lift capacities, both naval and air, as well as enough naval assets that they could easily defend any convoys that could be heading for Iran. If they were to follow the Entebbe model, it would mean C-130's or airliners carrying commandos to the target, the commandos destroying the target and returning to Israel the same day. I do not see an Israeli invasion of Iran, not now or ever. It's not that they could not do it, it is simply that the international reaction might well be far more difficult to deal with. A raid is possible, but an invasion, although somewhat possible for a short period of time, is a non starter.
3. Naval Raids. The Israeli Navy is of necessity a small ship navy, but they do have some missile boats that really are corvettes, At 86 metres long, there is no reason that these ships could not sail to the Persian gulf and have a bit of fun. Of course, after doing anything in the Persian gulf, it is highly possible that the Egyptians would not allow them to use the Suez Canal or that the Israelis would not want to expose their ships to some Egyptian or Palestinian crackpot with a few RPGs so the course the ships would take would probably bring them around the southern tip of Africa. That's a looooonnng trip. In addition the subs that the Israelis are having built could possibly be used. I found this tidbit on the net: "Foreign publications have even speculated — without evidence — that the Dolphin, and its sister ships Leviathan and Tekuma, may be outfitted with strategic capabilities." It would not be difficult to imagine that at least one of the subs has vertical launch tubes, and with those, a quick strike against Iran becomes easy. But it would still be a loooooonnng trip.
4. Nuclear strike. "nuff said.
Dean.