I use ExecuCar (http://www.execucar.com) wherever I can. They serve all three DC-area airports (DCA/IAD/BWI). They're owned by Veolia Transportation, who also owns SuperShuttle and some tour bus lines nationwide. Generally in the middle of the pack price-wise, and nearly always immaculate newer (1-3 yo) sedans. About one out of five rides they pick me up in an SUV for no extra charge.
My usual fare from the house to my home airport (PHX) is $61 each way (I'm about 25 miles from the airport).