Build your singlespeed or fixie bike around Surly's New Quick-Release Fixed/Free Rear Hub. This gorgeous hunk of aluminum has the capability you need and reliable sealed bearings, too! It sports threads for a track cog and lockring on one side and a freewheel on the other so you can decide how you want to roll. Plus, this hub's 135mm width fits most MTB frames and the chromoly axle provides a flex-free ride.
Also available in Silver (image unavailable from manufacturer).
Track cogs, lockrings and freewheels sold separately.
This hub is drilled for 32-spoke wheels.