Armadillo Aerospace

Deserves a special place in the hearts and minds for people interested in Mars for several reasons:

-John Carmack is the author of Doom, a first-person-shooter game that has its settings on... Mars. -Having become wealthy, he started Armadillo Aerospace, first to take a chance at winning the X Prize, but after encountering difficulties decided to restart all over again and eventually end up with a rocket that is capable of SSTO