I had an email from lastminute.com today telling me about this. There are other routes available too.
Travel from 25th August 2008 to 30th June 2009. Must book by 23rd September 2008.
I also tried this on the British Airways site for a test and flying Heathrow to JFK on 1st Oct '08 returning 8th Oct '08 was £298.50.
Click on go to deal to see all the other routes listed on the lastminute.com website where you can do a flexible dates search to find the cheapest deal.
Alternatively go to the British Airways website to double-check prices.