I completely agree with the value of having students memorize passages and speeches.  I teach English Language Arts, and I always make my students choose an at least fifteen line poem to memorize and recite.  Poetry is extremely effective for students to practice public speaking in terms of rhythm, cadence, and clarity of diction.  A really interesting idea to consider in correlation with your speech assignment would be to ask the students to work in pairs, having one student memorize a historical speech and the other student to find and memorize a poem that has content or a theme that complements the other student's speech. 

For example, one student could memorize an excerpt from Martin Luther King's "I Have A Dream" speech, and the other student could recite Maya Angelou's "I Know Why the Caged Bird Sings" or Langston Hughes' poem "Dream Variations."  You could even include a written analysis piece at the end in which the students must compare and contrast the two different texts, or have other pairs of students evaluate the presentation and decide what the similarities and differences are. 

What I would ask of you, in addition to what you have chosen and what has been offered, is that you offer more women's speeches.  Surely contemporary women have important things to say.  Hilary Clinton,  Barbara Jordan, Margaret Chase Smith, Betty Friedan, Eleanor Roosevelt, Shirley Chisholm, Indira Gandhi, Princess Diana, Maya Angelou, current Supreme Court women--just look for people your students can identify with the person or the ideas.  I believe that students are influenced by what we do, and if we don't present the idea that women are also a huge part of history, historical change, or involved in human rights, we do a disservice to all our students. 

Here are the sites for these.  Thank so much!

 Abraham Lincoln                      The Gettysburg Address        

http://showcase.netins.net/web/creative/lincoln/speeches/gettysburg.htm

Thomas Jefferson                   The Declaration of Independence      

http://www.archives.gov/exhibits/charters/declaration_transcript.html

Martin Luther King, Jr              I Have a Dream

http://www.americanrhetoric.com/speeches/mlkihaveadream.htm

Patrick Henry                                  Give Me Liberty

http://www.history.org/almanack/life/politics/giveme.cfm

Atticus Finch                                   Closing remarks to the jury

http://ncowie.wordpress.com/2008/03/23/atticus-finchs-closing-argument/

Winston Church                              We Shall Fight on the Beaches

http://www.winstonchurchill.org/learn/speeches/speeches-of-winston-churchill/128-we-shall-fight-on-the-beaches

Lou Gehrig                                      Farewell to Baseball

http://www.famous-speeches-and-speech-topics.info/famous-short-speeches/lou-gehrig-speech-farewell-to-baseball-address.htm

John F. Kennedy                             Inaugural Address

http://www.bartleby.com/124/pres56.html

Chief Joseph                                   Surrender Speech

http://www2.gsu.edu/~eslmlm/chiefjoseph.html

Marc Antony                                    Funeral Oration

http://www.dl.ket.org/latin1/things/holidays/ides/brutus.htm

Susan B. Antony                              On Women’s Right to Vote

http://www.historyplace.com/speeches/anthony.htm

Well, after carol-davis's exhaustive contribution there may be little to add! I think she missed Kennedy's Berlin speech: Kennedy speaking at the Berlin Wall, "Ich bin ein Berliner," West Berlin, Germany June 26, 1963. There is also Franklin D. Roosevelt's "Infamy Speech," December 8, 1941:

Yesterday, December 7, 1941 - a date which will live in infamy ...

Hamlet's "To Be or Not To Be" speech is always a challenging one: Shakespeare, Hamlet.

Perhaps the best thing I can add is to say which ones I like best. That would be "Ich bin ein Berliner" and "Infamy Speech." These give a profound sense of critical historic moments by capturing how one representative man thought and felt about the world and its state of affairs at that moment in time. These also show the power of the Presidency and give a porthole view into what our country's great past leaders have been like so as to provide a light into what our country's present leader needs to be like.

I, too, must commend your "gusto." Many students are not required to memorize speeches, or even poetry, any longer. They tend to only "remember" enough to get them through a test and forget the information.

My suggestions are:

1961 Kennedy Inauguration Speech

You said that the Declaration of Independence was not a speech. Actually, many Americans would have experienced it that way, read by someone at a public gathering. Many contemporary copies of the Declaration include diacritical marks suggesting how it should be read aloud. So it is perfectly reasonable to include it as a speech, and I applaud you for doing so. Another example might be the opening to the Crisis by Thomas Paine, which also would have been read aloud to many people. Another great speech from history is the "Cross of Gold" speech to the Democratic Convention by William Jennings Bryan. Finally, Eisenhower's address (linked below) to the American troops about to invade Normandy is brilliant--it too, was published in written form, but read aloud to troops by officers. It is also relatively short. 

First, I admire that you are asking them to memorize. We so seldom ask them to use that part of their brains. When I taught speech, I had my students do something like this. 

You certainly have a great beginning of speeches. Here is a list of some speeches that I am familiar with in quality.  Several of them will need to be cut down considerably.  All of them  have something good to say.

Patrick Henry                                  Give Me Liberty

Atticus Finch                                   Closing remarks to the jury

Winston Church                              We Shall Fight on the Beaches

Lou Gehrig                                      Farewell to Baseball

John F. Kennedy                             Inaugural Address

Chief Joseph                                   Surrender Speech

Marc Antony                                    Funeral Oration

Susan B. Antony                              On Women’s Right to Vote

Edward VIII                                    The Woman I Love

Harold Ickes                                     What Is an American?

William Faulkner                               Nobel Prize Acceptance Speech

Elie Wiesel                                        Nobel Prize Acceptance Speech

Edward Kennedy                             1980 The Cause Endures

Elizabeth Cady Stanton                    The Destructive Male

Oprah Winfrey                                  54th Emmy Awards

Sojourner Truth                                Ain't I a Woman?

Winston Churchhill                            Blood,Toil, Tears, and Sweat

George Graham Vest                         Tribute to Dogs

Martin Luther King, Jr.                      I’ve Been to the Mountaintop

Gen. Douglas MacArthur                   Farewell Address to the Congress

Douglas MacArthur                           Duty, Honor, Country

Franklin Delano Roosevelt                 First Inaugural Address

Ronald Reagan                                  Shuttle “Challenger” Address

I believe that all of these speeches can be found on line to copy.