British Airways and American Airlines have a flights sale from Dublin to North America so you can book return business class flights from around £850. For example:
New York - €1080
Boston - €1079
San Francisco - €1334
The outbound journey to North America must commence between the following dates:
23rd Dec - 2nd Jan
27th Mar - 12th Apr
1st Jul - 31st Aug (i.e. the entirety of the school holidays!)
22nd Nov - 30th Nov
You must start your journey in Dublin (but there are loads of deals on flights to Dublin at the moment so you shouldn't have any difficulties getting there). This is particularly good for July and August where economy class fares are expensive because of the school holidays so you can travel business class for only a little extra of the equivalent economy class flight starting in London.
Book by 27th January 2015 (although the offer could be pulled before then). You can also book through other booking agents like Expedia.