How to get the most of your power.
The newest craze in cycling has to do with making the power you produce go to making you go forward. The bicycle is one of the most efficient machines ever made (over 98% efficient for a nice bicycle in good condition), and can't be improved upon significantly. So, bike makers have turned to making the bike more efficient by making it slip through the air better. It may seem like a silly way to try and make a bike go faster, but it's not. This design idea is most visible in the type of race called the time trial. It is one man, by himself, racing against the clock. Aerodynamics come into special consideration here because there are not other riders around to break the wind (in packs, aerodynamics become less of an issue because within the pack, the air is almost moving with the riders, so the rider doesn't have to cut much wind).
Rider in a time trial race. Note the aero handlebars, solid and deep-rimmed wheels, the shape of the bike, and the goofy aero-helmet.
There are a number of ways to reduce the drag produced by bike and it's rider. The most common way is with aero handlebars. These but the rider in a low tuck over the bike, reducing his profile to the wind. This is the most effective way of making you more aerodynamic (you can make yourself go as much as 2 miles per hour faster by some studies. That doesn't sound like a lot, but trust me, it is)
Using deep-rimmed wheels also cuts down on a lot of drag. The spokes of wheels tend to churn the air, making them less aerodynamic, using a deeper rim will shorten the spoke, along with making the rim itself more aerodynamic. A totally solid wheel is the most aero-wheel, that can be used, but they are heavy, can catch cross winds easily. For these reasons they are only popular in the time trials.
Finally, changing the shape of the bicycle frame can make it a little more aerodynamic. By making the tubes in airfoil shapes and tucking non-aero shaped parts out of the wind, a slightly faster bike can be made. This makes the bike a little faster, but not as much as the other methods.
People who are lucky enough to get paid to ride a bike will often use aero-helmets as well. These funny looking teardrop shaped lids do actually cut down on drag a good amount, but don't protect the head much and are pretty expensive, keeping them out of the hands of normal folk.
A pair of deep-rimmed wheels
A rider going into an aero tuck