So, one of the big obstacles towards living on Mars is the planet's lack of a magnetosphere.
Mars had one, once, but it's "cooled off." There are a few places on the surface where there are localized magnetic fields - and colonies could theoretically be positioned within them. Other than that, anyone living on Mars would be completely exposed to the radiation of the solar wind. (Other solutions would be protective domes with magnetic fields in them, living underground, etc).
So, how about giving Mars its own magnetic field, artificially? Dr. Jim Green suggests this might be possible. You'd need to place a spaceship at a L1 point that created a magnetic "tail" surrounding the planet. A big spaceship.
The neat part? JUST giving Mars a magnetosphere would warm the planet, thicken the atmosphere and potentially render the planet habitable.
In the nearer term, artificial magnetospheres could be used to shield space stations and craft from radiation...or make those magnetic domes I was talking about earlier.