There's lots of discussion of equipment in this thread. Let me talk a bit about route selection.

You know the best route to drive to work, but that doesn't mean you know the best route to ride to work. Your ideal route will avoid busy streets as much as possible. That means that instead of taking the big, broad streets and highways favored by cars, you'll take the side streets that run parallel to those big streets.

In many cases, you won't know about these streets. As a driver, you've been avoiding them. They are out of the way, and they might be difficult to reach with a car. So, get yourself a map. That's right: Look at a map of the area where you've been driving through for the last 10 years of your life. You might discover something new, or something you forgot about before.

Your goal in route selection is not always to find the shortest route. Your goal is to find the easiest route -- the route that is the safest and least aggravating. Over time, your tastes might change; it took me a year before I was comfortable with riding in heavy traffic, so during that time I added 2 minutes to my commute by taking a side street two blocks out of the way.

Remember that you have options available to you that cars do not. For cars, one-way streets are huge obstacles. For you, dismounting and walking a block down a one-way street might shave several blocks off your ride. (Do not ride on the sidewalk, or ride the wrong way on a one-way street!). For cars, driving through parking lots, parks, stairways, and buildings is a no-no. For you, it's all a possibility.

How do you spot these shortcuts? Again, it starts with a map. But also, when you finally do choose a route, keep your eyes open. Do you notice that concrete barrier the neighborhood erected to keep out cars? You can ride around it.

If you are lucky enough to live someplace that has a helpful bike trail, use it. When I started commuting, I didn't think it was worth my time to ride a half-mile out of my way to a bike trail, so I instead took a route through heavy traffic and multiple stoplights. That route was shorter, but ultimately not quicker--and probably not safer. Life is easier without cars, traffic lights, or exhaust.