I don't know ALL the MTB parts that are interchangeable, but have used MTB cranks, cassette's and RD's on my road bike. I have even gone to the extreme of (gasp) using a Campy BB with my XTR crankset! I liked the idea of cartridge bearings in the BB, and even using ceramics for it.
Like Retro says, your BB has to match your frame (68, 70, or 73mm width), but beyond that, you can mix 'n match to your hearts content. Of course, your BB has to be the type your intended crank will fit (square taper, ISIS, etc.).