May is Bike Month in NYC and there are plenty of bicycling events going on in and around New York City. BikeMonthNYC.org has the most comprehensive coverage, including an Event Calendar.

The Tour de Brooklyn is a leisurely paced, 18-mile bike tour along a relatively flat route that starts May 25, 2008 at 9:00am.
Registration is free and required. [there's a 2000 person limit on the ride]
Day-of Event Registration will be available at New Dock St. and Water St. in Dumbo from 8-9 am on Sunday, [...]

The Bicycle Film Festival is coming to NYC: May 28 – June 1, 2008. The Bicycle Film Festival is a celebration of bicycles through film, art and music. more info at bicyclefilmfestival.com

Bike Month celebrates the fun, convenience and ease of cycling in NYC. Here are just a few of the great rides, workshops, and events of Bike Month.