Iceland Express currently have very cheap single tickets from New York (Newark) to London (Gatwick). It's not direct but the layovers aren't aggressive and for £150...well I think it is worth the wait.
Using this return, I was able to book my outbound and inbound flights separately for £130 less than any comparison website or individual airline was offering. Might be of more use to those planning last minute breaks than those who plan months in advance, but thought it was worth mentioning.
EDIT: Doesn't seem to like the link but flights in from July onward seem to be this price right now