[Taz-in-Space]

anyone know any other possible, non-FTL engines? no unknown science, predictable technology only.

Well, I read somewhere that it is possible to use controlled nuclear explosions as an engine.
Sort of a putt-putt-putt engine with a nuclear explosion as each putt!
Just don't get too close to the business end!!

As anyone can guess this tech would require massive shielding; but should allow a large payload...

As far as the likelyhood of colonizing other planets - I think that if a habitable planet is descovered (or made) and the tech exists to get there reasonably easy; then colonization WILL happen. It will be inevitable!