What is the best website to find cheap flights to England?

I work for Dohop, a small Icelandic software company specializing in finding cheap flights. We search pretty much all prices available anywhere, and are generally considered very good for finding cheap flights outside the USA, and from the USA to other countries.
What we do and many similar websites do not is search not only all prepackaged routes, but also routes where you can effectively self-connect – basically find a lower fare by organizing your own connecting flights. This may mean you need to make two or more separate bookings (depending on how many stops you have) but you will possibly save quite a bit of money.