Today marks the 20th anniversary of the now famous Ronald Reagan speech, where he encouraged Secretary Gorbachev to "tear down this wall". That wall fell later after he was out of office, but the close proximity of the words and the deeds lead many to believe that this one speech was very instrumental in the dream becoming a reality.
Growing up during the Cold War, no one really gave much thought that they'd ever see a reunited Germany, much less the fall of the Iron Curtain. But, Reagan had a vision and wanted to see that vision become reality, to facilitate a brighter hope and future for those that lived under the oppressive Soviet empire and create a more peaceful world.
How much of that came because of him will no doubt be the subject of many debates well into the future. Where a person stands on that issue will depend entirely on the politics of that particular person. But to deny that Reagan played any part in that event, simply denies the reality of the situation.
Here is an interesting article on that speech and how it compares and contrasts with some others.
Also here is a list of 10 interesting facts about some other famous presidential speeches.