Aside from Orion (definitely not going to happen) and NERVA (almost definitely not going to happen for earth to orbit) I don't think there is much that's likely to be viable in the near future. <br /><br />The only things I can think of are scramjet first stages (great for reusability but nothing revolutionary in terms of payload capacity) and, even further off, that thing with the lasers where they heat initially air and then later in the flight rocket propellant. I've seen a video of that going a few hundred feet into the air but it is a long way off launching anything into orbit.