I'm really looking forward to the new Harry Turtledove alternate history novel. My understanding is that in it, France and Britain went to war against Nazi Germany in 1938, rather than allow Hitler to conquer Czechoslovakia. Thus Hitler was not as prepared as he would have been a year later.
Here are some other alternate WWII scenarios that I'd like to see:
1. US/UK and USSR go to war in June, 1945.
2. Germany invades Sweden in 1941.
3. Germany invades Switzerland in 1941/2.
4. Germany gains the upper hand in the Battle of Britain and launches Operation Sea Lion -- the invasion of Britain.
How about you? What alternate history scenarios (WWII or otherwise) would you like to see novelized?