Just posted this on our blog, and thought there might be a few people here who will be traveling Aer Lingus.
Starting July 14th, Aer Lingus will change its baggage policy for long-haul flights (including, those from the US). One bag is free. Additional bags will cost $50 per bag.
If you purchased your ticket before July 1, 2009, you fall under the old luggage policy and will get to check your second bag at no additional cost.