My vote would have to go to HBO's magnificent miniseries John Adams, in which an American lawyer, against all his inclinations and growing desire for independence, defends the accused British soldiers following the Boston Massacre. Adams' argument states the men had a right to defend themselves after being harassed by an angry mob with ice balls, clubs, shells and rocks, along with his closing argument which stated that "facts are stubborn things" and "a sentry's post is his castle" has to put this one at the top for me.
Closing arguments and Verdict: http://www.youtube.com/watch?v=Iyrv5emDC1Y
EDIT: Please link the speeches if you can, I'd like to watch them!
Other great speeches:
Atticus Finch closing argument, To Kill a Mockingbird http://www.youtube.com/watch?v=k8TgqenWW0I
"Miss Jean Louise, stand up. Your father's passing."
Originally Posted by WonkersTHEWatilla
Mr. Rogers defends PBS to the US Senate.