'Well, SpaceX is still playing the "expendable rocket" game, at least for the moment.'
As much as I am an enormous fan of non-chemical-rocket approaches into space (as hartror linked), they all fall into one of two categories: "Not proved feasible" (space elevator and all variations thereof), and "Contains the word 'nuclear' and not proved feasible". I break that second one out as a separate category on the grounds that making many of these proposals functional seems a lot more likely than the more far-out ones, but are Utterly Impossible because nobody will even fund research into a space technology that contains the word "nuclear", let alone permit it to fly. We barely get RTGs into space, because they are the only solution, and not without ignorant protesters nearly managing to stop it.
For instance, I'm a fan of the nuclear lightbulb [1]; I don't know if can be built or not, and I suspect I will never find out, because nobody within my lifetime will try, despite the fact it may require no actually new physics or technology.
If you're trying to make money in this field, best start with the things we actually know will work. Let us all hope the multi-trillion-dollar-market-cap SpaceX of 2040 see its way to funding some of these proposals, goodness knows our governments aren't going to until the word "nuclear" completely loses its fear factor.
Oh, and if we all die because we're hit by a meteor that could have been stopped with a nuclear lightbulb or even Project Orion, let the record show I hate you all, humanity.
[1]: http://en.wikipedia.org/wiki/Nuclear_lightbulb