The best cameras for Northern Light photography are full frame DSLRs with a fast fixed wide angle lens. The next best thing is a DSLR with a cropped sensor. Now there is a new breed of cameras that is excellent for the travelling photographer. They are called "mirrorless cameras" and I see more and more people using them, and with good results. Check out this blogpost from the excellent photographer and blogger Chase Jarvis. He had Sohail Mamdani write a review of the most popular mirrorless cameras:
DSLR Killers — Mirror Mirror on the Wall, Who’s the Best Mirrorless of Them All?