Faraday, Ampere, Tesla, Maxwell - great contributions to the electromagnetic theory and application. Faraday was such an awesome guy on practical applications and learned a lot on his own, working in Davy's (another great guy) book store.
Benjamin Franklin, Coulomb - Electrostatics
Shannon, Fourier, Laplace, Gauss - The geniuses who developed a lot of mathematical theory for communication. Any one of them would be my my pick for the greatest. I just cannot describe the genius and beauty behind Fourier's contribution
Kilby - Though the invention of transistor in itself was very very significant, the idea of integrating them into chips was pioneered by this guy. Great contribution.