August has been recorded as a peak date for meteor showers for centuries. Tiny grains of sand entering the Earth's atmosphere glow so brightly, they look like falling stars. And every year at the same time, we go through the same field of sand grains, and the show starts all over again.
The Perseids (called that because they originate in the sky near the constellation Perseus) are considered one of the biggest meteor showers of the year. On a clear, dark night, there might be as many as 50 shooting stars per hour. They'll peak tonight after midnight, and may also be visible on Friday and Saturday. Get out there and take a look. Maybe even make a wish.
The darker it is when (and where) you're looking for falling stars, the more you should see. The moon phase can make a big difference: the less moonlight, the better your view. This year, we're in luck: the moon is just a sliver, and it will set relatively early. Artificial light is also very important: if you can, go somewhere away from artificial light sources. Your darkest bet in DC might be Rock Creek Park; the Capital Astronomers like to use the field just south of the intersection of Military and Glover Roads NW. (In fact, they'll be there on Saturday night.) The problem is, the park is officially closed after dark. If you've got an idea for safe, legal, less-lighted locations that have open sky, we'd love to hear about them.
In general, you'll see the most meteors in the time between midnight and dawn. (That is, if you're enough of a night owl or early riser to be seeing anything then.) This has to do with how the Earth is moving in space: in the early morning, we're moving toward the part of the sky you can see, and thus there will be many more visible collisions between meteors and our atmosphere.
The final thing you'll have to consider is the weather report. Clouds, obviously, will make it much harder to see the meteors. But so will humidity, which creates a haze that makes it harder to make out anything in the sky. Not to mention, a nice dry night makes it much more pleasant to be outside.