Leeched this list off MTBR:
Out of box 650b compatible:
WhiteBrothers 650b forks
2008 Fox RLC/FX
Any 29" Suspension fork
Any Rigid fork with a AC longer than 360mm
manitou R7 (2006 tested)
All Fox Forx (some forks may rub so slightly on the bottom of the crown if all the air is removed)...