I have one answer:  The Second World War.  In my mind, the results of both rulers can only be secondary to the fact that they helped immerse Europe in WWII.  Both leaders sought to increase the political will of their nations through overtaking other nations, forming alliances that threatened much of Europe, and posed a direct and challenge to the liberalized democratic structure of the rest of the world.  A more theoretical result of both rulers' reign was that it proved rather conclusively that allowing one individual so much power without any form of legitimate institutional check can bring about more bad than good to any political setting.  If one considers this, it makes sense because we point to an increased centralized government as being bad, "Like Hitler or Mussolini."  Both leaders have become quite synonymous with destructive centralized authority gone too far.

Well, Nutella was invented in Italy so the results weren't all bad...

There were some effects that have not been mentioned by the previous posts, one was a rather anti-religious backlash in Germany as a great deal of what the Nazis were appealing to was a sense of righteousness and an idea that God wanted them to take over Europe and change the way it worked to a system that they wanted.

Another is a change in warfare and some of the things that people considered to be acceptable in terms of how a war is conducted.  Prior to the war, the idea of firebombing an entire city with the purpose of killing as many inhabitants as possible with little regard to military targets was repulsive and even barbaric.  During and after the war it became somewhat accepted by the mainstream and was even glorified in propaganda films etc.  One author recently gave his book the subtitle "the end of civilization" in order to suggest what he felt were the effects of that conflict.

Another could be the rise of the Soviet Bloc and the changes that affected Eastern Europe that are still important today in trying to understand how that part of the world works.

The first answer is absolutely correct with respect to the impacts of their rule on their respective countries.  I want to talk a bit about their impact on the world.

Hitler, in particular, had a huge impact in that he (more or less) started WWII.  Because of this, you can say that the result of his rule was nothing less than the whole second half of the 20th century (and aspects of today).

For example, without WWII, Western Europe is not devastated and the US and USSR do not become rival superpowers in the Cold War.  Instead, you have various powerful countries, including Germany, France, and Great Britain.

WWII totally shaped the world we live in and that is an important result of the rule of these two men.

That's a pretty broad question, but the only way I can really answer that is that both of their countries were physically, economically and socially devastated.  Hitler's "Thousand Year Reich" lasted all of 12 years, and when it was done, he was dead, all of Germany's major cities were leveled by bombing, and over 8 million Germans were dead or missing.  A mere 5000 Jews remained in the entire nation and Germany was completely conquered and occupied, then divided for 54 years.

Italy fared little better. Mussolini's new "empire" struggled to conquer Ethiopia and lost almost everywhere else they fought. Again, hundreds of thousands died, and parts of the country were smoking ruins. It would take years for them to climb out of economic desperation. Mussolini and his mistress Clara Petacci were shot and then strung up for passersby to spit on. Quite the legacy.