I'm pretty sure that things would'nt be too different if Hitler had'nt existed.
The treaty of Versailles peed off a lot of Germans, and it wasn't just Hitler that wanted Germany to rise up and get it's revenge, right after WW1 there were a lot of attempts to take over Geramny, not just Hitler, there were uprisings almost constantly in the early 1920's from both left ad right wing groups (Some parts of Germany were even taken over by communists at one point I think), so even if Hitler had'nt existed, I think there would have still been plenty of nutters who woul'd have started an uprising and taken over Germany and formed a dictatorship which would then starts a world war eventually, but not in the form of the Nazi party.
Perhaps, if Hitler hadn't risen to power, there might have been a communist uprising in Germany, eventually resulting in alliance with the USSR which probrably would have led to a longer cold war instead of a WW2.
Perhaps a civil war would have erupted in Germany in the early 1930's (due to the effects of the wall street crash causing problems for Germany, causing its people to turn to the extreme political parties), or early 1920's, as left and right wing groups struggled to gain power over Germany, perhaps Germany would split up as the states it was formed out of had uprisings and declared independance (similar to how Yugoslavia split up perhaps).
Technology would certainly not be as advanced, as said above in this thread, war drives the development of technology.
Aircraft would not be so advanced, jet engines would have taken longer to come into use, radar would also probrably have taken longer to develop, and the atomic bomb probrably would'nt have been develped so soon.
I reckon that the moon landings would probrably not have happened until the 1980's or later even.
Perhaps also, if WW2 had not occured, then the USSR would not have occupied Eastern Europe as the Red Army pushed the Germans back Westward, perhaps that would then mean that the Warsaw pact would not have been formed.
Perhaps Italy under Musolini would have started WW2 instead of Germany.
Who knows, there are so many different things that cause events in History to happen, so what would have happened is anyones guess.
