There is now a nice, green policy that is being followed in as many as 21 European cities that is not yet being followed in a single US one that I am aware of, having just googled a bunch on the matter. It is a city bike system, also sometimes generically called a "Velib" system after the very popular and famous one in Paris that began in 2007. However, while it is doing very well (see the Wikipedia entry for "Velib" about it), it has some oddities that may make it less desirable for cities in the US thinking of adopting such a system, it being run by a private company for the city.
Probably the oldest running, since the 1970s, and the best run is the one in Copenhagen, where nearly 40% of trips are now done by city bike. The city (actually through a non-profit organization) owns bikes that are kept in parking stands. In Paris they make you pay a subscription, and then you can access the bikes, which are locked up in their stands. In both the stands are all over the city, but in Copenhagen they are free. You just pull one out and ride it to another stand. Reduces traffic, improves health, reduces pollution, and any city in the US would look very cool and progressive and innovative if it were the first one in the country to do it. The bikes tend to be three speed and pretty tough with a good-sized basket in front. The biggest problems have been with car traffic, and in Copenhagen, with cars turning right and not paying attention to bikes coming up. Anyway, a nice link about the Copenhagen system.