When I went to Orlando earlier this year we took a town car recommended by the DIBB from MCO to our hotel. I was very impressed by the service and it worked out as cheap as - if not cheaper than a taxi. Has anyone a similar recommendation for the trip from IAD into DC itself given the distance and lack of seamless public transport?
Try http://www.limos.com
However, I did public public transport from IAD to the city and it was fantastic, cheap and very easy too

Washington Flyer Bus Service from IAD to West Falls Church Metro station then The Metro into the city
Very cheap and pretty quick too. mcmbenjamin recomended these options for me when I was there in March and I would use them again for another IAD trip. I actually spent longer in the immigration queue than I did travelling on public transport into the city!!!
Regards