Both in the near and far future what engines will drive “fast” interplanetary ships?

the newest system on the horizon is a nuclear/ion engine. they are being used on a couple of space probes as we "speak". they only work in a vacuum, so they have to be launched by chemically propelled rockets. they accelerate VERY slowly, but can run for years. a hydrogen/fission motor may be used for a manned mars mission. an onboard fission reactor wold give crew members lots of electrical power, and the engine could cut travel times to mars by 50%, or more.

Future space ships will travel at the same speed as the current ones or possibly slightly faster.

M2P2 propulsion will make conventional solar sails a thing of the past, check out the links for some interesting reading.

All answers would just be conjecture. Look here for some possibilities:

http://en.wikipedia.org/wiki/Interplanetary_travel