This price currently available for:
27/5/08 - 5/6/08
31/5/08 - 5/6/08
31/5/08 - 7/6/08
Direct flights Heathrow to JFK with Kuwait airways.
Can't get a direct link - but just search for LON to NYC from the homepage.
Just booked this myself.
There are some deals at similar prices for departures before end of April. But for late May / early June, this is the cheapest I could find by at least £100.