Depending on the type of plane, here are your options:
IAD- approximately 35-55 minutes from downtown, via the Dulles Access Road and Route 66, depending on traffic and the time of day. Signature and Landmark are the FBOs. 27 miles to the "mall".
JYO (Leesburg)- approximately 45-60 minutes from downtown, via the Greenway extension, Dulles Access Road, and Route 66. Landmark is the FBO. 40 miles.
HEF (Manassas)- approximately 45-60 minutes from downtown, via Route 66. Jet Services and Dulles Aviation are the FBOs. 35 miles.
FDK (Fredrick, MD)- approximately 60-75 minutes from downtown, via Route 270 and the Beltway. Traffic varies greatly but if business is on the north side of town, this or GAI (Gaithersburg, MD) (45 minutes) might be the best option. FDK- 51 miles, GAI 31 miles.
RMN (Stafford, VA)- approximately 60-75 minutes from downtown, via I-95 and I-395. Near Quantico and Fredricksburg, VA on the very southern suburbs. 46 miles.