Located west of the city, Washington/Dulles International Airport provides more choices for the traveler to use than Reagan National. Many international flights along with cross country flights takeoff/land here.
There are two airports to get you to Washington DC. I have only flown into Dulles Airport. It has been renovated lately, as the airport is abit dated for an International Airport. BE prepared for security checks since 911 and even more so now, since the Iraqi war.
I have always had to make a connection at another location (except when flying Air Canada direct from Vancouver to Washington.)
The other Airport, Ronald Reagan Airport is located closer to the city center than Dulles.
Map and directions to Dulles (above)
It is not at all easy to get between Reagan National and Dulles. If you must do so, I strongly recommend you allow at least 5-6 hours between flights. But if you must, here are my three recommended options, from cheapest to most expensive:
1: Go to the airport Metro station, buy a ticket to Rosslyn, take a free "Metrobus Transfer" from the push-button machine just inside the fare gates. Take the Blue Line (direction: Largo Town Center) to Rosslyn. Exit Rosslyn and ask the Metro attendant how to get to the "5A" Bus. Go to the bus stop and board Bus 5A to Dulles Airport. Fare ranges from $1.60-$2.35 for the Metro to Rosslyn, then $6 for the bus ride from Rosslyn to Dulles Airport. If you have a Smartrip Card, you get about a 75 cent discount.
2: Go to the airport Metro station, buy a ticket to West Falls Church. Take the Blue Line (direction: Largo Town Center) to Rosslyn. At Rosslyn, take the escalator downstairs and change for the Orange Line (direction: Vienna-Fairfax) to West Falls Church. At West Falls Church, follow the signs to the Washington Flyer bus. Metro fare to West Falls Church is between $2.15 and $4.10, depending on time of day You get a 25 cent discount if you use a Smartrip Card. One-way fare on the Washington Flyer from West Falls Church to Dulles is $10.
3: Arrange for a shuttle van to drive you from Reagan to Dulles. A good choice is SuperShuttle. They are offering a private van between the two airports for up to 7 people for $150. Take a look at http://www.supershuttle.com for details if interested.
Baltimore/Washington International Thurgood Marshall Airport (or "BWI" for short -- also its Airport Code), is about 30 miles (50 km) northeast of Washington. Most domestic budget flights arrive at this airport. A hub for the U.S. budget carriers Airtran Airways and Southwest Airlines, BWI also receives flights from 14 other airlines, including international carriers Air Canada, Air Jamaica, and British Airways. Daily direct service is available from Toronto and London-Heathrow to BWI. There is also weekly nonstop service from BWI to Ghana, Nigeria, Jamaica, the Dominican Republic, and Mexico.
PUBLIC TRANSPORTATION: Metrobus B30 departs from BWI to the Greenbelt Metro Station every 40 minutes. Cost is $6. You pay by feeding your money into the machine next to the driver. $1 and $5 bills are accepted, but no change is returned. Travel time is about 30 minutes to Greenbelt. From Greenbelt, the Metro ride downtown takes about 30 additional minutes. Fare from Greenbelt to L'Enfant Plaza in Washington ranges from $2.75 to $4.65, depending on the day and time of your trip.
RAIL: From the terminal, you can take a free shuttle bus to the BWI Rail Station. From there, you can take either the MARC Commuter Train ($6, approximately every hour Monday-Friday only, 40 minutes) or the AMTRAK train (roughly every hour, fare varies but usually $14, 25 minutes) to Washington's Union Station.
RENTAL CARS are at a separate facility. A free shuttle will get you there from the terminal in 10 minutes.
TAXIS to Washington are prohibitively expensive, though shuttle van service is available. Check the website below for details.
One final note: You cannot go between the Domestic and International terminals without passing through security. While there is an excellent food court inside the Domestic terminal, the lone food stand inside the International terminal is terrible.
Ronald Reagan Washington National Airport (Airport Code: DCA), or "National" as it's known by locals for reasons of brevity and/or politics, is by far the airport most convenient to Washington. Just across the river from the city, Reagan National Airport is the choice of business travelers and politicians. A hub for US Airways, it also receives flights from 10 other US carriers as well as Air Canada. Reagan National Airport only has direct flights to destinations in the USA and Canada, though international travelers can arrive at the airport after arriving in another airport (such as Philadelphia) and transferring to a domestic flight.
PUBLIC TRANSPORTATION: Reagan National Airport has its own Metro station, served by the Yellow and Blue Lines. The Yellow Line in the direction of Fort Totten will take you directly into the city. Fare is $1.60 or more, depending on your destination and time of day. Tickets can be purchased from machines outside the Metro gates; credit cards are accepted.
RENTAL CARS: Shuttle buses can take you to your rental car, though it's only about a 1/4 mile (500 meter) walk to most companies. However, some companies, such as Thrifty, National, and Enterprise, are more than 1 mile (2 km) away on Jefferson Davis Highway.
TAXIS are very expensive. A taxi ride downtown will normally cost $20 or more. Unless you have a lot of luggage, the Metro is a much better option.
Dulles International Airport (Airport Code: IAD) is located approximately 25 miles (40 km) west of Washington, DC. If you are flying to Washington from outside North America, this is the airport you will most likely use. A hub airport for United Airlines, Dulles Airport also receives flights from 38 other airlines, from Aeroflot to Virgin Atlantic.
While there are a mind-boggling number of terminals, arrival is easy, if not lightning fast. If you are arriving from an international destination, you will be directed to one of two uniquely-shaped "mobile lounges" for the ride to Customs and Immigration. One "mobile lounge" is for passengers arriving in Dulles; the other is for those transferring to other destinations. After you pass Immigration, you will continue on to Customs to pick up your luggage and declare any dutiable items you're bringing into the USA. You will then find yourself in the common reception area to continue on to ground transportation.
PUBLIC TRANSPORT, while improving, is still quite limited. Metrobus 5A departs every 40 minutes (once per hour weekends) from Dulles (lower level) to the Rosslyn and L'Enfant Plaza Metro stops. Cost is $6, pay on the bus by feeding your money into the machine next to the driver. $1 and $5 bills accepted, but no change is returned. Your other option is the Washington Flyer bus that departs every 30 minutes from Dulles (upper level) to the West Falls Church Metro station. Cost as of February 2011 is $10 ($18 for a round-trip ticket), pay at the booth before you board the bus. Credit cards accepted.
RENTAL CARS: There are a great many car rental companies that serve Dulles Airport, but all of them are located a significant distance from the airport. Marked shuttle buses will take you from curbside to the appropriate parking lot. Once you get your car, there is a designated toll-free road that will take you to the Beltway and Interstate 66.
TAXIS: Only the Washington Flyer Taxi is allowed to pick up passengers at the Airport. Cost from Dulles to Washington is approximately $65 plus tip.
Ronald Reagan International Airport has to be one of the United States' nicest. It was my first time using it and it was a pleasure. We flew from Fort Lauderdale to Ronald Reagan Airport on US Air and though it was not a direct flight, since it was a fairly short one, it was pleasant enough and at approximately $180 R/T each, about the least expensive we could find.
The airport is quite pleasant and with a huge US flag dangling down from its rafters, I can't imagine a better way to enter the city than by air and by arriving at this very airport. It is also very easy to get into town from Ronald Reagan as it is on two Metrorail lines. It was the reason we chose Rosslyn to stay as it was on the one of these lines as well. The ten minute trip costs only $1.45 each. Though common in Europe, this is one of the few towns that has good rail service to its airport.
Coming in from THurgood Marshall airport you can take the Greenbelt Express Bus to Greenbelt Metro Station to Washington DC and the appropriate subway line to where you are staying. In our case our stop was Waterfont.
Take a couple of things into consideration. This airport reminds me of DFW-Dallas/Fort Worth. If you are renting a car, the car rental terminals are offsite, so you must take a free bus there. Add on the time to turn in your car and about a 15 minute bus ride to the airport when factoring how early you have to arrive for your flight. I found the check in and security lines to move relatively quickly. Also, in order to get to many of the terminals you have to take a mobile subway car on wheels(this is the only way I know how to describe it) from the main terminal. This is about a 5-10 minute ride, so factor this in too.
We flew into Dulles, took the Washington Flyer to the Metro, then the Metro to Smitsonian stop and a short walk to our hotel. It was a 2 hour trek during rush hour,after the flight, with luggage. It wasn't the worse thing in the world, but the airport had some sort of "moving lounge" ,the Washington Flyer bus was nice and easy to find, but a long wait and :30 minute ride. The Metro was almost :45, I didn't realize it would take that long.
By far, the nicest airport to fly into is DCA (Reagan National Airport), but it can be a HUGE hassle. Flights into/out of DCA are often very expensive and are sometimes reserved for government officials ONLY, but it is a small airport and a metro stop away from just about everything. If you can swing a cheap trip into/out of DCA, then go for it.
That being said, I recommend flying into BWI (Baltimore, MD) and then taking the metro into DC. It's way cheaper and far less of a hassle, especially if you have someone there to pick you up.
Finally, IAD (Dulles, VA) is an option, but it's normally quite expensive and more out of the way.
SAA flies daily to Dulles, Washington DC from South Africa. The flight makes a stop over at Dakar. It is a very long time on the aeroplane, but you don’t have to catch a connection flight. Flights leave from OR Thambo Int Airport, Johannesburg.
Another option is to fly with Delta, via Atlanta.
You didn't say which day, but there is a 4:50am 5A bus Monday-Fri and the earliest on the weekend is 5:30 from your location (L'Enfant Plaza). As the other poster has said, you will be cutting it really close using the the 5:30 bus to catch a 7am flight at Dulles. I live by Dulles and go out there regularly. You have to also figure in checking in your bags and getting to your gate in your timing and if there are a lot of people at your airline counter. Depending on airline gate location, you may be running through the terminal. Alternative is to take a taxi or arrange a limo service from your hotel. With the distance being traveled from DC to Dulles, both are going to cost about the same.
MY favorite airport here by far is DCA. It is closer to the city and AA has good service here. Paired up with a metro connection and extremely easy access to Alexandria, Arlington or downtown Washington you could easily make a quick trip into the city on a long layover or wait longer before leaving on your next trip out of there.
Washington DC has no airports within its tiny territory, but there are three airports in the surroundings that offer access to DC from either Virginia or Maryland. Reagan Airport is located in Arlington, Virginia, and it's the closest one to DC from all the three, plus you can access this airport by metro (either the blue line or yellow line can take you there). Both international and national flights arrive and depart from there. Its closeness to the city has raised more than one complaint to the inhabitants, due to its proximity to the neighborhoods and the constant roaring of airplanes going to and coming from this place.
If you prefer to take a taxi from Reagan Airport to DC, instead of using the metro, the fare would go around US$11- 20.