It's no secret that I am a huge fan of the bicycle. I don't think, however, that I've enumerated the multiple reasons why this is, including some that aren't readily apparent.
Lots of people have gone over the obvious benefits - primarily, that you save money on gas, get some exercise, and produce only the Carbon you exhale. However, the benefits go beyond that.
I ride a bike because it saves me time. This probably seems counter-intuitive; bikes are slower than cars, right? While this is true even of an expert cyclist against a mediocre car, the difference is that I am accomplishing two things at once when I bike. Given that I've spent most of my life either overweight or obese (mostly the latter), I consider exercise to be extraordinarily important. Given that, my options for getting to and from work are:
drive to work: 25 minutes
drive to the gym from work: 20 minutes
work out: 60 minutes
drive home: 15 minutes.
total: 120 minutes.
Alternately, I can just ride, whereby I get to work and work out at the same time. That looks like the following:
Ride to work: 50 minutes
Ride home: 50 minutes
I save 20 minutes, AND get almost twice as much exercise.
As I mentioned before, bikes make landscapes better. Take your typical big box store (in my head I'm thinking of Fry's). It's a dot of a building surrounded by a sea of parking. If a substantial portion of people rode bikes there instead of driving, these buildings could be closer to one another, and not look like retail islands in an asphalt sea.
This actually addresses one of the most common reasons people cite for not biking, namely, that things are too far away. If we didn't dedicate so much space to the automobile, we could place buildings closer together. Considering that most cities which predate automobiles have buildings placed very close to one another, and mix residential, retail, and commercial space, it would seem that this is how humans chose to arrange themselves before an artificial barrier to doing so came along. If you think of cities that are the best places to visit or live, I'd venture that you don't think of suburbia.
Lastly, biking strips away the anonymity of being in a metal cage. This may seem small, but humans are social creatures, and the brief "hello" or smile can go a long ways towards your (or my, at least) psychological well-being. In addition, it's harder to be mean to someone you recognize as another individual, and not just an anonymous box.
