The October Revolution was extremely significant with the White movement losing to the Bolshevik movement, but most important of the 20th century is hard to determine.
I would barely disagree. The People's Republic of China defeating the Republic of China, I think, is a far more dangerous and long-lasting effect that can be noticed across the world, and their dictatorship will probably be in for a very long time. The question, I think, is whether the PRC would be better or worse if their founder did or did not model themselves after the USSR, and if they would have still won. Nobody can know that, though, unless a time traveler would please stand up at this 01/04/2012.
Current dictators who study the USSR would be limited to studying the past, but they can look all the way to the Chinese civil war and far beyond for inspiration from the PRC. I'm sure even the DPRK copied the PRC more than the USSR. I'm mostly convinced that the PRC's longevity will make it more influential by the time it finally dies out, if and whenever that is.