Google recently unveiled a new bicycle map feature on its Google Maps. The bicycle route mapping is a beta version and Google is looking for user input.
Google says in a news release that the feature "provides step-by-step, bike-specific routing suggestions – similar to the directions provided by our driving, walking, or public transit modes. Simply enter a start point and destination and select "Bicycling" from the drop-down menu. You will receive a route that is optimized for cycling, taking advantage of bike trails, bike lanes, and bike-friendly streets and avoiding hilly terrain whenever possible." More information is available here.
Here's the link: http://maps.google.com/biking. Google maps also has a feedback function that allows you to report unmapped bike routes, streets that aren't ideal for cycling or other problems. Below is a video explaining the new Google Bike Maps feature.