Similar in minimalist philosophy (if not in form) to JRuiter + Studio's city bike is this Gravity Bike by Jeff Tiedeken, a.k.a. Monkey Likes Shiny.
As you can see there's no drivetrain and the crank has been locked, with the pedals replaced with mere foot peg holders. In testing, Tiedeken has reportedly done 60 m.p.h. plus on this thing. Someone get this man a GoPro camera.
There's a Flickr page full of shots of the finished product here, and MLS has a blog entry from last year featuring the prototype shots.