We will not invade Syria or Iran. Unlike defeating a failed state (Afghanistan) and one tattered by 15 years of sanctions (Iraq), Syria and Iran are organized enough to create, at least, a more drawn out conflict. Our military is also pretty much as stretched out as it gets right now, so they don't exactly have the room (or budget, for that matter) to start a four-front "war on terror."
In terms of Iran, a matter of patience could yield a rather liberal government in a generation or two. The best course of action in Iran, probably, is to lob a few missiles at their nuclear facilities if the UN determines that Iran is a nuclear weapons threat. Israel did this to Iraq in 1981.
Syria would probably fall quicker than Iran, considering that even Israel's military capability dwarfs that of Syria, but again, unless you're interested in another protracted and expensive insurgency, it would probably be best to leave Syria alone, while continuing to keep an eye on it and continuing to freeze assets of likely offenders.
Melon