Dwight D. Eisenhower exit speech on Jan.17,1961. Warning us of the military industrial complex.
http://www.youtube.com/watch?v=8y06NSBBRtY
I don't know if it was the best or not. But I think it was a VERY important one that too many people forget.
Mine was the one never given. George W. Bush's resignation speech after impeechment proceedings were started and after Chaney had died of his 21'st heart attack.