boston is chock full of fixed gears and singles.. sometimes i think i see more of those than road bikes and mountain bikes.. but that's probably because i pay more attention to them. you also see plenty of recumbents and other funkie bikes.. i once saw a double bike.. it's hard to describe. i believe it was one frame welded on top of another, so the guy had to climb up someone else to get in the saddle. it was a sight. there's also a sideways bike i see around, where the guy sits perpendicular to the direction of movement.