I always use Dulles Taxi service http://www.dullestaxi.com/ when I want to go from my place to the Dulles International Airport. Iv found their service to be very prompt and friendly. When I called first, they just got my address and were very punctual for the pickup. The next time I called them they had my info on file and it was painless. Their charges are far lesses than the other ones and they dont charge extra for a Car Seat in the car. Thats something important to me as I have a baby travelling with me.