Always like that (don't know why) but you can still book to fly in to one city and out of another as one return flight. Most websites have a "multi-city" option (should be next to the return/one way option) so you can just enter Shannon-Chicago outbound, Seattle-Shannon inbound or whatever. Worth you while checking out a few sites too even though Aerlingus is often as cheap as anyone. I always check expedia, orbitz and kayak as well.
Another option is try www.ba.com with routings direct from Cork airport, click the "Book Multi City" option. BA flights involve taking the (Aer Lingus) flight from Cork to Heathrow, but you can book your bags the whole way through from Cork to your final destination.(and the same on the return leg). The other advantage is that if anything goes wrong with flight delays, they have to get you there.
In your case Jim, what might be a better option, is to book a multi city: Flight 1 from Cork/ShannonDublin to Chicago, Flight 2: your flight home from Seattle to ireland with one carrier, such as BA or Continental, Delta etc.
Then, assuming you are not driving from Chicago to Seatle ! You could book a single flight between these two cities with a budget U.S. airline such as www.jetblue.com or www.southwest.com and you will find these are fairly inexpensive even for single trips.
Last edited by Falling At Your Feet; 13-09-2011 at 12:45 PM..