If you want to try bicycling on the cheap and support keeping waste out of landfills, consider restoring a discarded bicycle as your next project. While the time and money investment will vary depending on the condition of the bike, you still should save a decent chunk of money and will have learned essential repair skills.
Instructables user schkip1973 provides a knowledge base for learning to restore dumpster bikes by recommending specific bicycle repair books, tools, and materials to have on hand, taking you through stripping down the bike into parts, restoring the frame, and reassembling the bike.
Of course your found bicycle's may also have problems with the wheels, brakes, gears, etc. While this particular instructable does not go into those details you should have no trouble finding similar tutorials online or in the recommended bicycle repair manuals.
There are lots of salvageable bicycles in most every town or city. If you need a ride or you're looking for a new hobby why not give bicycle restoration a try?
Restoring a Vintage Dumpster Bike | Instructables
Leaving a high-priced bike locked up in the city can often be a frightening task if you don't know how to do it properly. Thankfully, Bike Habitat's Hal Ruzal has a guide to not just locking up your bike, but blocking people from taking parts too. 
Sure, pedaling your bike can get you from one place to another, but a user at DIY web site Instructables details how you can really put all that effort to good use by charging up your USB devices.
Ever find yourself out with a biking partner (that is, two bikes) but just one lock? Make demonstrates how easy it is to make do with one lock for both bikes.
