Biking strengthens, tones, burns off calories, and relieves stress. It also reduces your carbon footprint by conserving precious fuels that are better spent building new bicycle factories (whose products will lead to even more fuel conservation, and so on). And biking costs you precisely $0 per gallon, saving you buckets of cash. Although today's Groupon for the Marin Kentfield FS is not $0, it's close enough—and pretty much a steal, given the quality of Marin bikes. The Kentfield FS is especially perfect for commuters, but will also serve you well on a rigorous workout sesh or a leisurely Sunday ride. A lightweight aluminum model, it only weighs 27.5 pounds, so even those who are flabby of bicep can lift it with minimal effort or strain. While its 700 x 35 tires translate into smoother rides, its powerful brakes will help you stop safely. Finally, its Shimano shifters and derailleurs will provide the control and flexibility you seek as you shift between its 21 gears.