Kurt Refsnider gave a thumbs up to the White Brothers carbon rock solid fork in this write up he did about his 2011 rig.
http://salsacycles.com/culture/kurt_refsniders_2011_tour_divide_setupOn the front end, I mounted a White Brothers Rock Solid rigid fork with an aluminum steerer and carbon legs. While it’s not the lightest rigid fork out there, the fore-aft flex in the round carbon legs absorbs washboard vibrations better than any other fork I’ve ridden. Should I ever race the Divide again, you’ll see me on this same fork.
From the picture below it looks like Ollie Whalley used a Niner rigid fork up front to win the race in 2012.
I've been looking into different ways to setup my own bike and a rigid fork will be one of the options. Not sure which one yet.