Help!

I am trying to book flights to the US for after Christmas - London- Dallas, Chicago-Manchester (or London if it's a ridiculous request). I'm checking Travelocity, Expedia, STA and BA. Anywhere else I should be looking?

Thank you very much! I went with travelocity in the end, because I started to develop a conviction that by the time I'd checked everywhere the flights I wanted would be sold out. I had also tried the student travel agent on campus, but they offered me two non-direct flights for about £50 more than I eventually booked three direct flights (with no nasty early morning starts) for.