Moots Psychlo-X Road and Cross Bicycle
The cross terrain design Pscyhlo-X is a titanium giant. It will take you from road to mud without a flinch. Some of many many features of this ~17lb bicycle are: replacable rear hanger, front derailleur pulley and barrel adjuster to swap out off-road and road derailleurs, wishbone mono-stay eliminates seat movement under breaking, top-routed brake and shift cables, and a carbon fiber pitch fork. Oh, and it looks killer.
Cost: $6,000 @ Moots
Also See: Review on Wired.com