I have a book at home, the name of which eludes me, that is basically an anthology of ATLs written by a few historians. The Cuban Missile Crisis was an interesting one.
Soviet commanders had recieved release orders from Moscow, something we didn't know at the time. A Soviet submarine could employ a nuclear torpedo without requesting authorization and the Soviet commander in Cuba could have launched his IRBMs the same way.
The POD for this ATL was that a Soviet submarine DID launch it's nuclear torpedo when it was pinged by an American destroyer. (In OTL, the commander held his fire, although he had prepared the torpedo for launch.)
The resultant nuclear detonation over the horizon led to immediate air strikes by the USAF in an attempt to knock out the missiles in Cuba before they could be launched, an effort that failed. Four missiles flew, one that detonated over Washington DC, one that missed and landed in farmlands in western New York, one in (IIRC) Atlanta, and one dud. With Kennedy and most of the government destroyed, command fell upon the commander of NORAD who ordered a total nuclear retaliation. The Speaker of the House was located later that day, who confirmed the actions of generals.
American response was a total launch of IRMBs out of Italy, Turkey, and Great Britain, followed by ICBMs out of the US and bomber fleets winging towards the Soviet Union. At this point, the Soviet leaders did not even know about the launching of nuclear weapons by their forces in Cuba (Soviet communications systems were poor at the outset, a loss of contact for periods of time was nothing out of the ordinary).
Major Soviet cities, military bases, and other assets were immediately destroyed by missiles. Eastern European countries saw their capitols go up in smoke, along with any Soviet military bases within their countries, but otherwise were untouched. Bombers patrolled over the Soviet airspace, looking for targets worthy of nuclear bombardment. This lasted for three days before the majority of American strategic assets had been exhausted and the pleas of European and Asian allies to cease firing were heard.
The following year, exploration teams from Europe entered into what was formerly the Soviet Union, finding less than 10% of the population still alive, the rest dead to either direct nuclear affects, radiation poisening, starvation, or societal collapse. The nuclear attack on the Soviet Union became known as the Second Holocaust.
The United States is ejected from the United Nations and demands for reparassions from the affected nations (Europeans mostly, suffering fallout) fall on deaf ears, as the United States felt it was the aggreeved party.
Was a very interesting ATL, scary in some ways, but I'm gratified to know that we could expect the US to have survived a nuclear exchange in 1962.