Also usually named by the "pro-diplomacy crowd" are Saudi Arabia, Turkey, and Jordan - Iraq's Sunni neighbors who all have a stake in the stability and overall (territorial) integrity of Iraq. However, there is one major country in the region that has received almost no attention despite its size, influence, Sunni denomination, and contribution to radical Islam: Egypt.

Sadly, the United States and the rest of the West are so fearful of what real political change might mean in Egypt, that we will likely acquiesce in the ensconcement of Mubarak's successor (likely his son Jamal) in Cairo's halls of power when his father passes. As we have for the last 25 years, the US will probably place its hopes in the powerful Egyptian security services' ability to suppress dissent -- and there is no bigger indictment of US foreign policy than that. And don't even bring up the half-hearted "pro-liberalism" trip that the Secretary Rice embarked on in 2005. Unusually blunt though US criticism might have been, the estimated nearly $2 billion in annual economic and military aid provided to Egypt sends a much louder message.
Ok, so having said all this, what does it have to do with Iraq. Simply this,
How on God's green Earth can we even begin to think that we can "convince" Syria and Iran to act in good faith and "common interests" in Iraq if we can't even get Egypt, a coreligionist to Sunni insurgents, run by a government fearful of Islamic radicals, and a recipient of over $50 BILLION in US aid over the last three decades to take any meaningful, public action to support our efforts? Using a "carrot" approach, we can't.
Looking at the longer term, (intensive) US engagement in Iraq will end at some point (my guess is late 2009) and we can and will leave the country. Redeployment will end some of our problems and allow us to wait out the Iraqi aftermath. My worry is that when Egypt goes south, however, Israel will not be able to pack up and redeploy. And that, unfortunately, is where we come in...
And that is also why we will continue to kick the can.
[Sorry that this was so "stream-of-conscious-y". There are a lot of threads I'd like to get around to pulling one day -- WMD, geopolitical competition between Egypt, other Sunni states, and Iran, and re-alignment of US foreign aid priorities. Perhaps when Dr. C goes to do his residency I will tag along and settle-in to writing a dissertation on one of them.]