Rent a Bike in Europe for Nearly Nothing
Paris is rolling out 10,600 bicycles for the public to use practically for free. Similar public bike programs can be found in Lyon, Brussels, Vienna, Helsinki, Oslo, Copenhagen, and elsewhere.
OSLO, BERGEN, TRONDHEIM, AND DRAMMEN (NORWAY)
Again, you'll need a Citybike tourist card to ride the public bikes in Oslo, Bergen, and Drammen. (Note: Their systems only operate on a seasonal basis, usually shutting down in late fall and reopening in the early spring.) City visitor information offices rent the requisite cards out to tourists.
In Oslo, though, there are some important differences. Oslo's Bysykkel program charges tourists 70 kronor, or about $10, a day. Rentals are a maximum of three hours. After three hours, you have to return it to a bicycle station, but it is possible to rent the bike for another three hours without paying an additional fee.
Note that, when biking, you must stay within Oslo's city limits. Stations will only allow you to take out bikes between 6 a.m. and midnight. They will give you merely 30 seconds to pull your bike from its stand once you've been assigned one—but they will accept bike returns 24 hours a day. (When bikes are properly returned to a stand, a little light in the lock changes from red to green.)
In Trondheim, Norway, people can use a free bike simply by popping in a small coin into the lock, which pops back out again once it's locked back up. More info for the programs in all of these Norwegian cities at adshel.no.
Denmark's capital has 1,300 free bikes for the public to use annually between May and mid-December. All you have to do is find one of the 125 City Bike stations in the city center and deposit a DKK 20 coin (about $3) and start pedaling (staying within the city center). You'll get the coin back when you lock it back up at a City Bike station. Details here.