One rule: People saying Einstein must give a runner up also, or else I think this thread will be 99% Einsteins, and boring.
My vote is for Max Planck. I mean, he made up quantum physics in a few hours. He’s got to get lots of credit for that.
Richard Feynmann, natch. (I’m betting there will be quite a few votes for him as well.)
He did a lot of work on quantum mechanics, including his own pet theory QED (quantum electrodynamics). He was also a first class educator, perhaps the finest physics teacher in history. His printed lectures are big sellers to this day. He was also one of the guys who worked on the atomic bomb, and was on the commitee that figured out why the Challenger blew up.
In addition, he was [Steve Martin voice]“a wild and crazy guy!”[/SMV] Artist, bongo player, lady’s man, world traveller…his autobiographies are hilarious.
Oops! Only two n’s in “Feynman”, not three.
I gotta go with Feynman too. His autobiographies (IIRC “Surely you must be joking, Mr. Feynman” and another one) are a hoot. He goes on about safecracking while working on the atomic bomb, among other things. He seems very human, not at all pretentious, and just a generally good guy. Plus he was brilliant.
Well, geez, I thought I was going to get to be the first to mention Feynman, but almost everybody has so far! But it’s still true; not only was he brilliant, but he was hilarious and had an anti-authoritarian streak that’s very appealing.
Da Vinci. Feynman was nice, but he couldn’t paint.
I’m the first to say Stephen Hawking? Come on, he punched Homer Simpson in the face, for crying out loud! How many scientists can say that?
He couldn’t paint, but he could draw! Even sold a few pieces, and had a one-man show, according to his books.
And Da Vinci never played in a Brazilian samba band, or translated a Mayan codex, so 
!
Charles Darwin. Quite a rabble-rouser, that one.
Maybe not, but he did draw. Professionally, even. In Surely You’re Joking, Mr. Feynman!, there’s a section of chapter 5 called “But Is It Art?” that talks about his “career” as an artist.
Stephen Jay Gould, just for his popular writings. The man was a doper, whether he knew it or not.
Daniel Dennett. Funny I always got the feeling that Feyman was arrogant and that his modesty was completely false.
err Feynman.
Feynman–SYJMF has to be one of the funniest and most inspirational books at the same time. A man like that doesn’t need modesty.
But, saying as everyone else has mentioned Feynman already, Richard Dawkins. His books, especially The Blind Watchmaker have done the most to make evolution theory accessible to non-scientists.
He also built a Robotic Exoskeleton, and is an accomplished gangsta rapper.
Personally I’d have to say Carl Sagan, not only a well-regarded scientist/researcher in his own right, but arguably the most successful person ever in bringing science to the public.
Then of course there are the world-shakers as it were, who stand along with Einstein as some of the greatest scientific minds in human history.
Democritus
Eratosthenes
Sir Issac Newton
Johannes Kepler
Galileo Galilei
James Clerk Maxwell
Charles Darwin
Edwin Hubble
Richard Feynman, of course. He was my father’s faculty & thesis advisor at CalTech, and I’ve met the man. Too bad I was too young to realize just who I was talking to… I have a copy of the Feynman Lectures autographed to me by the man. It’s one of my most prized possessions.
You may all kiss my toes now…
Something else DaVinci didn’t do that Feynman did: Crack safes and drive military security insane for fun.
Backup choice ( and Intaglio’s favorite, no doubt 
) would be John Nash.
Me.
James Clerk Maxwell
-Justhink
Lise Meitner.
Well since nobody else has said it I’ll go with Julius Sumner Miller. Damn that guy definitely had the look of the mad physicst.