When I have to do a short IAD layover I usually pick either the Holiday Inn Express or Hampton Inn as an economic place for just a bed. Both are about 10 min away have shuttles to the airport. The Holiday Inn has a restaurant & Irish-type bar & is a bit nicer than the Hampton (no facilities other than the comp breakfast but it's just across the street from the HIX) but I normally pick the Hampton for the Hilton stay credit.

If you are a Priority Club member the Holiday Inn will give you a comp breakfast too but you usually have to ask for it at check-in.