It's a tough question which I know has been addressed a couple of times at bikeforums.net - try searching there. The back is fine, any rack that is good for any other bike will be fine. It's the front that's the problem, the fork is a slightly weird shape, ruling out a few common options.
Fwiw, Topeak super tourist dx has worked well for me in the past (especially with topeak rack bag), but I pretty much go rackless these days. Even managed to squeeze the christmas presents into the frame bag today