By some miracle this hasn't already been nominated, so:
After 1900
1945
Decisive Darkness: What if Japan hadn't surrendered in 1945? by The Red.
It has never actually won a Turtledove, despite last year getting I think the second or third highest number of votes of anything on the entire site!
After 1900
PODs in 1940 and 1944
Stars and Sickles - An Alternative Cold War Hrvatskiwi
A massively overlooked timeline.