If you're looking to make the trip across the pond to America, then finding a reasonably priced flight shouldn't cause you too much hassle. After all there are plenty of flights to America from Ireland every single day leaving from both Shannon and Dublin, so lets check out your options.
If you'd been flying as recently as 2008, you'd have been able to enjoy direct flights between Dublin and LA, as well as Dublin and San Francisco, however Aer Lingus has cancelled these routes as they weren't quite profitable enough. Aer Lingus still runs quite an extensive route of US flights every day though.
The Irish flag carrier flys daily to New York a whopping three times from Dublin, with one of these flights stopping off in Shannon. They also fly directly to Washington, Boston and Chicago daily, with seasonal flights to Orlando in the summer. There are also direct flights every day from Shannon to Boston every day. Check out aerlingus.com for more information and bookings.
If the deals on offer from Aer Lingus aren't tickling you pink, then check out what American Airlines can do for you. American fly daily from Dublin to Chicago, and often offer brilliant value deals. You can also fly Dublin to Newark in New Jersey daily with Continental, and Dublin to Philadelphia daily with US Airways.
Check out http://www.skyscanner.ie for the best deals on these flights, and even more options on getting to America, including connecting through London Heathrow.