I recently just received my first new commuter bike for my birthday (gift from SO's family). I didn't own a car for five years, and I used a free road bike, an early 90s steel frame. Now, I use a cyclocross, which is faster and more nimble than a hybrid, but more rugged than a road bike. In my experience, there are several things you want to find in a commuter bike:
1). Thin tires that can handle imperfect road conditions. That usually means road bike, cyclocross, hybrid, or touring. I would avoid mountain bikes, too heavy and tough on hills. Road bikes are most expensive, followed by touring, cyclocross, and hybrid, generally. Road bikes are the quickest, but most expensive and least rugged. I like cyclocross because my bike is nimble and light, but has thicker tires and some other options that make it zippy.
2). Water bottle holder. Drink up!
3). Good headlights and tail lights.
4). The range of gears you need for a comfortable ride. While I know some folks who enjoy fixie (one gear) bikes, I need a range (like 18 speed) to comfortably manuever hills and whatnot. I'm no primo athlete, just a bike commuter.
5). Some way to carry stuff. Either a nice backpack with moisture wicking back, or a rear rack with room for a crate, bag, or cooler.
A lot of the other stuff are bells and whistles. I would pick a price point and find the best possible bike you can within your price range that matches your criteria. If you can, test ride, because all bikes feel differently and go to a pro bike store and get yourself fitted. Every bike model and make are different, so its important to understand your size needs. Finally, get a biddy to ride with you (motivation), learn the easiest and safest route, and don't be shy to use public transit or other modes as a complement. What make bike commuting doable for me is flexibility; when it rains or tired or whatever, I take public transit.