A blog entry at Colony Worlds describes this problem, and a possible solution, which is to use artificial magnetic fields for settlements. This idea is not new. Other than providing extremely fast transport through the solar system, the M2P2 drive is designed to shield the passengers of a space ship from radiation. Such an drive would give potential settlers much easier access to places such as the inner moons of Jupiter (Io and European in particular).
The idea seems to be catching on as scientists are about to test a new "deflector shield" which creates an artificial magnetic field to deflect harmful radiation.
Another option is the transhumanist one, which is to modify the human body itself to withstand radiation.
Now scientists at the Rutherford Appleton Laboratory in Oxfordshire plan to mimic nature. They will build a miniature magnetosphere in a laboratory to see if a deflector shield can be used to protect humans living on space craft and in bases on the Moon or Mars.
In order to work, an artificial mini-magnetosphere on a space craft will need to utilise many cutting edge technologies, such as superconductors and the magnetic confinement techniques used in nuclear fusion.
Thus science is following science fiction once again. The writers of Star Trek realised that any space craft containing humans would need protection from the hazardous effects of cosmic radiation. They envisioned a 'deflector shield" spreading out from the Starship Enterprise that the radiation would bounce off. These experiments will help to establish whether this idea could one day become a practical reality.