"U bikes" is awesome as already posted. Also check out Sports Garage on Spruce. Some fixie riders there too.

A guy there invited me to join them on a century "mystery route" group ride on July 4th this year. They don't announce the route until the day of the ride, but at 100 miles it sounded like a blast (or a death ride...not sure which). I was out of town so I missed it.

I ride 2 brakes, got big decents and freakish drivers.

I'm east of town so not totally dialed on the boulder scene, but there are lots of riders around.

Check out the thursday night cruiser ride in downtown if you are into that sort of thing. Draws a pretty big crowd. Go to the Rio Grande, get a marg and hang on the patio...you can't miss the ride from there.