The expected benefits of riding to work versus driving are pretty obvious: fun, fitness, saving money on gas. And these are great. The feeling of joy when riding is not to be discounted, and getting 80 minutes of incidental exercise a day is nothing to sneeze at, well, unless you live in Austin, the allergy capital of the world. [insert pity chuckle here]
The most surprising thing I have noticed is how easy driving feels after cycling. Usually driving feels like such a chore, but after actually using your body to get you from point A to point B, having a machine do the work for you feels pretty luxurious.
The next most unexpected benefit was increased interactions with people around me. Everyday I was out I met someone, sometimes two people. And this was usually on the way home, when I inevitably ride a lot slower. Although very cursory interactions, they are important in this over-connected, under-connecting modern world we live in.
The last unexpected side effects was not hating red lights as much. Though they do suck when you're going real fast and have to stop or want to make them but can't, on a bike, the red light can be your friend. A nice moment to sip some water and rest, look around. And that's the real overall benefit to cycling more: seeing more, feeling more, being more.