Fixed gear bikes have become very fashionable in many cities around the world.  Essentially paired down ultra low maintenance bikes first favored by bike messengers, they are characterized by a single gear, no freewheel, and often no brakes (which is quite dangerous but I guess part of the thrill).  I have never (yet) tried one but will be documenting the scene anyway.  To start with, here is a promotional video from Charge(a UK bike brand) featuring Juliet Elliot (one of their team riders) who does a remarkable job of explaining fixies and why they’re cool.  In my opinion, she’s really cool too :-) .