Off the top of my head, Benjamin Franklin, Albert Einstein, Gautama Buddha, Carl Sagan, and Leonardo da Vinci.
Honorable mentions are Nikola Tesla, Abraham Lincoln, Teddy Roosevelt, Amelia Earhart, George Carlin, Mark Twain, Aristotle, Gandhi, Emerson, and more.
Actually, there's really no order to that. Just off the top of my head. The reasons are that we could use some polymaths who just "got (stuff) done", or who were future-thinking or completely innovative for their time.
Me, I would have to choose Benjamin Franklin, Thomas Paine, Bill Hicks and George Carlin because the world, America in particular, could really use their wit and wisdom right now.
Can't decide on the fifth one.
Edit: Einstein, I guess.
I think that's a really good list, at least from a USA perspective. Much of my list is from a US perspective as well.