All of a sudden, bike-share programs have popped up on cities across the country. Which is awesome, because exploring a new city by bike is, well, awesome. While cities like San Francisco and Nashville have trial programs in the works, these four are already running. Last April, Denver became the first U.S. city to open a major bike-share program, allowing visitors to link spots like the art museum, the botanical gardens, and Coors Field. Denver.bcycle.com. In Minneapolis, Nice Ride Minnesota, which launched in June, offers 65 rental stations and 700 bikes. Follow one of its mapped routes, published on its Web site, connecting breweries and urban art fixtures. Niceridemn.org. Chicago's B-Cycle opened in July and has six stations along the Lake Michigan waterfront, with easy access to beaches, the aquarium, the planetarium, and the Field Museum of Natural History. This spring the city hopes to expand to 50 stations and 1,000 bikes. Chicago.bcycle.com. In September, Washington, D.C., and Arlington, Virginia, opened the largest program to date, with 1,100 bikes and 114 stations. Zip between museums, cruise the trails through Rock Creek Park, or head to the Potomac and rent a kayak. Capitalbikeshare.com.