+1 for Jonas Salk. Smart people really should be smart enough to be nice, if you ask me. Giving the world the polio vaccine was a nice thing to do. I'd say he has to be my all-time favourite.
Einstein and Boltzmann were visionary. Boltzmann was ahead of his time - Einstein SHOULD have been ahead of his time, but suddenly everything was moving so quickly anyway

The scientist I read most of (in my free time, at least) is Sean Carroll. Apart from doing interesting theoretical work (cosmology, time) he's a great science communicator, e.g. this fascinating blog that he writes (with some other people):
http://blogs.discovermagazine.com/cosmicvariance/