The BA/Iberia/American Airlines transatlantic joint venture have this delicious fare for those who travel light.
Certain Spanish cities (including Madrid, Barcelona and Palma de Mallorca to East Coast USA (New York or Boston) for just €266 if you travel by hand luggage only. If you use checked luggage you can expect this fare to go up by around €80, but even still €346 is a good effort.
You can further improve the flight-only deal by adding in 3 nights of hotel stay on Times Square, New York which is going for €429 per person. Other slightly cheaper options are available, down to as low as €409 per person, though judging by the location this one looks best.
For those who are more adept with fare construction, this ticket is a “Maximum Permissible Mileage” fare construction. If you don't know what I'm talking about and would like to know more, read my tutorial on MPM surcharges.