John F. Kennedy gave the strongest speech of his young presidency in 1962 during The Cuban Missile Crisis. You can read the whole speech Here.
After the disastrous "Bay of Pigs" affair, Kennedy's credibility was in need of repair, but there was no feeling on the part of the American public that his speech, or the plans he outlined that night, were in any way political or self-serving. The speech was full of memorable lines, some very powerful.
Here's the quote:
"We will not prematurely or unnecessarily risk the costs of worldwide nuclear war in which even the fruits of victory would be ashes in our mouth; but neither will we shrink from that risk at any time it must be faced...
"It shall be the policy of this nation to regard any nuclear missile launched from Cuba against any nation in the Western Hemisphere as an attack by the Soviet Union on the United States, requiring a full retaliatory response upon the Soviet Union."
Ronald Reagan gave one of the most memorable of his speeches at The Berlin Wall in 1987. You can read the whole speech HERE.
One short admonition in that speech (written by Peter Robinson), was taken out and put back in by White House staff more than once, until finally President Reagan insisted that it stay in.
Here's the quote:
"General Secretary Gorbachev, if you seek peace, if you seek prosperity for the Soviet Union and Eastern Europe, if you seek liberalization: Come here to this gate! Mr. Gorbachev, open this gate! Mr. Gorbachev, tear down this wall!"
(If the video doesn't appear, you can watch on YouTube by clicking the below link:
George W. Bush spoke to the crowd gathered at the site of the fallen World Trade Center Buildings, three days after that horrific event of 9/11. Here's the video of his short impromptu speech that rallied that crowd and the rest of the nation, a nation of which he was proud to be the president.
Barack Obama spoke to the nation, on September 10, 2013, to outline his plan to address the situation in Syria. You can read the whole speech HERE. There were many memorable quotes from that speech.
Here are a few:
"So even though I possess the authority to order military strikes, I believed it was right, in the absence of a direct or imminent threat to our security, to take this debate to Congress...
"My answer is simple: I will not put American boots on the ground in Syria. I will not pursue an open-ended action like Iraq or Afghanistan. I will not pursue a prolonged air campaign like Libya or Kosovo...
"However, over the last few days, we’ve seen some encouraging signs. In part because of the credible threat of U.S. military action, as well as constructive talks that I had with President Putin, the Russian government has indicated a willingness to join with the international community in pushing Assad to give up his chemical weapons...
"I have, therefore, asked the leaders of Congress to postpone a vote to authorize the use of force while we pursue this diplomatic path."