When I was at Sycip Designs in Santa Rosa, Jeremy was in the midst of building up a bike with the Schlumpf internally-geared crankset. The Schlumpf has 2 speeds on a single chainring; you toggle from the 2 gear choices by tapping a button on the crankarm at the BB axis. This system is similar to the new SRAM/Truvativ crank for free-ride and downhill except the SRAM design uses a bar-mounted shifter and requires a specially designed frame.