Here's some options for May 20 - June 03, 2009
www.vayama.com - $815.61
Depart BWI about 4 PM EST - Arrive FCO about 4 PM Rome time; 1 connection each way...
www.continental.com - Various flights at $1,112; Many options available. 1 connection in most cases
Search through www.mobissimo.com and you will get many options including this British Air deal on Airfare.com:
British Airways BWI-LHR; 09:05 PM - 09:20 AM FL#228
British Airways LGW-FCO; 02:00 PM - 05:25 PM FL#2540
British Airways FCO-LGW; 07:30 AM - 09:10 AM FL#2545
British Airways LHR-BWI; 04:15 PM - 07:35 PM FL#229
Both of these BA flights DO REQUIRE going from LHR to LGW but there is PLENTY of time with 5 and 7 hours between flights!!! And the price at Airfare.com (working through mobissimo) is.... $861 .
This last flight (below) has an airport change ONLY on the return and with a 7 Hour layover, no problem. In fact, pretty darn easy - Total price $876.55 - Does have a long layover at LHR, but you could shuttle in London for lunch!!!
British Airways BWI-LHR; 09:05 PM - 09:20 AM FL#228
British Airways LHR- FCO; 06:15 PM - 09:45 PM FL#558
British Airways FCO-LGW; 07:30 AM - 09:10 AM FL#2545
British Airways LHR-BWI; 04:15 PM - 07:35 PM FL#229
I'm sure there are lot's of other options out there, but these are a few I found!I hate to see you book "separate" flights because if issues arise you could get stuck. If you book all on one ticket, you are far more protected!
Good luck!
Ron in Rome