Checked fares this morning and saw U.S Airways is offering round-trip flights from San Francisco to Dublin (DUB) Ireland for a base fare around $390 - $497 with all taxes & fees. Travel at this fare must commence on or after October 1st. A few flights on American and Delta pull up fares slightly higher - but still decent prices as well. Fare Basis TFA0NGOctober might be a great month to visit; just coming out of peak summer travel, but before the harsh winter. One valid trip at this price I checked on was October 24-29th, with a stop in Philadelphia.
Fare found on Farecompare and Orbitz and U.S Air
ALSO A GOOD DEAL...
San Francisco to San Diego $39 each way + tax on Alaska airlines through the summer (weekend travel permitted at this fare, though limited dates left)
Oakland (Or SFO) to San Diego $39 each way + tax on Southwest Airlines
(Southwest starts flying from San Francisco on August 26th)