personally I'd look around at the main airlines directly, Continental, Delta, American Airlines, BA, Air France, KLM, as well as looking at the Ebookers.ie and gohop.ie sites.
As for the advertised price versus the final price, it can be difficult for an airline to confirm a final cost as different airports charge different fees, what you will see also is that the more airports you visit during your journey the higher the final cost (ie via CDG can add EU70+).
The main benefit of flying directly from Ireland is completing US immigration in Dublin, when you get to the US airports its very nice to be able to pass the long queues at the desks there, but for a significant cost saving I'm sure you wouldn't begrudge queueing.