There's probably already a post or thread that covers this, but I can't find it. If someone points me at it I'll go read it!

I want to book a flight from *somewhere in England* to *somewhere in Florida*. Is there an online booking site that allows me to enter that as my flight details, rather than having to check every possibly combination of BHX-MCO, LHR-MCO, MAN-MCO, BHX-TPA....

It'd save me an awful lot of time, given that I can be very flexible about where I go from and where I land.