Washington DC Dulles IAD to London and Amsterdam are a couple of deals available today. Delta and United Airlines offer nonstop flights to Amsterdam in the $440s, but only from Feb 28 to March 31.
British Airways is $506 to Amsterdam or London Heathrow LHR. BA is the lowest alliance fare to London with departure dates Jan 19 to Mar 30. Amsterdam on British Airways at $506 round trip is higher than fares with Delta and United. Departure dates for Amsterdam are the same limited Feb 28-March 31 window as Delta and United.
United Airlines Washington DC Dulles IAD – Amsterdam, Netherlands nonstop flights
KLM Airlines Washington DC Dulles IAD – Amsterdam, Netherlands nonstop flights
British Airways Washington DC Dulles IAD – London Heathrow LHR nonstop flights
SkyTeam and Star Alliance are priced in $530s for IAD to London, but like Amsterdam the lowest fares are only for travel in March.