Where can I get cheap flights from Washington to London?

I am travelling to London next summer for a week, but the prices are unreasonably high... any clues?Where can I get cheap flights from Washington to London?
Try BA.com. They will list the dates and give you prices for seven days each way. Then take the cheapest day and try expedia.com; travelocity and see if they are any cheaper. Bear in mind the longer you leave it the more expensive they will get. We got a good deal last summer - try avoiding the peak days/time and you will get a cheaper flightWhere can I get cheap flights from Washington to London?
I've always had the best luck with travel agents. Contact one. They'll be able to compare all airlines.