George Washington Carver. Born into slavery in MO. Parents were bought by their owner for $700. Went to University of Iowa and studied botany. Synthesized many products from peanuts (a legume) and sweet potatoes. Taught at Tuskegee University. Died poor despite many inventions. Fascinating.

Richard Feynman. Manhattan project.
Nicola Tesla. Genius with electricity.
Thomas Edison. The other genius with electricity.
Max Planck. discovery of energy quanta won him the Nobel Prize in Physics in 1918.

Edward Witten - Unified string theory in what is now called M Theory.

Marie Curie, I suppose because she was a pioneer and a role model.

Ooh I love Neil deGrasse Tyson and Richard Dawkins, and just today I watched them having a mind-blowing conversation with each other (on youtube:

Is it just me or does anyone else get excited to go toe to toe with some evangelical that just knocked on your door?

Neil DeGrasse Tyson is my all time fave followed by Michio Kaku. Neil shares my love of the coshmos and he is just freakingly smart and logical. He has this ability to deal with the trolls that come to hear him speak during the question and answer section that is pure class. I witnessed his cool classiness in person when he spoke at Drake University. Of course the Christians send a child trying to get him to slip up and they failed. The man is BRILLIANT!

I've gotten to meet Lawrence Krauss a few times at conferences, Bill Nye at the Reason Rally and Neil DeGrasse Tyson and Richard Dawkins after speaking engagements and I'm "friends" on facebook with many fairly prominent scientists including both Sean M. Carroll and Neil Shubin and of course follow the other Sean Carroll and Jerry Coyne. But I gotta say Tyson is my favorite for shear personality and enthusiasm with Brian Cox a close second. Though I wish I had been aware and wise enough to appreciate Feynman and Sagan while they were still alive. As I get older I just get to be a bigger and bigger fan of science and keep giving my daughter hopeful nudges in that direction.

I liked Carl Sagan.

I really enjoy Neil Degrasse Tyson. He explains things in a way that most anyone can understand. I saw him earlier this year in Asheville NC, and he was hilarious. I also find Nikola Tesla fascinating.

I have liked many of those that have been mentioned and I will also add Einstein and Tesla.

Bill Nye, he may not be a scientist but he is out there pushing people towards reality. And you are definitely not going to beat the man in a debate. And of course Neil Degrasse Tyson the most lovable scientist to ever walk the planet.

All of them. As Newton said; "If I have seen further than others, it is by standing upon the shoulders of giants." Carl Sagan, NDT and Stephen Hawking are some of my favorites because they're able to put complex scientific concepts into terms normal people can understand. I grew up watching Bill Nye and Beakman's World and Mr. Wizard so I have a special place in my heart for anything that gets youth interested in scientific concepts and reasoning. Michio Kaku is fun and always leaves me looking forward to the future. David Attenborough is one of my favorite humans ever and who doesn't love Jane Goodall?

Dennet, Harris, and dillahunty is getting more popular but as a philosopher not scientist. Of course krauss and sagan and you've already brought up tyson.

Geeze ... I don't have one but I like Bill Nye. The rest of them are good. James Randi... I like him too. I could go and find some but I don't need them. I'm happy...