There were some crazy conventional technologies also. One scientist, as a joke, did a calculation about the effects of adding mercury to rocket fuel. It wouldn't react with the fuel, but it would add a lot of weight which would make the thrust more efficiently move the rocket forward.
This was tested, found to be true, and thankfully never put to use in any actual rockets.
http://en.wikipedia.org/wiki/Project_Pluto
Which is nuclear ramjet, which has the small side-effect of spewing large amounts of radiation as it flies.