Spanair has been selling seats on US Airways to Barcelona and Madrid for fares as low as $396 round-trip including tax. Most of the deals are for travel beginning October 23, but we even found peak summer fares for the low $400’s including tax.

 
Oddly, some of the best peak summer deals are leaving from New Orleans. We have no idea why.
 
And the travel date restrictions vary not just depending on departure city, but they’ve been changing from hour to hour. And as with any unadvertised airfare sale, these fares could disappear or change at any moment.
 
If you’re planning on spending a month in Europe, the sweet spot this summer is, for some unknown reason, departing on July 18 and returning August 17. That’s when the lowest fares are available in general, for summer travel. Some of these fares are as low as $500 round-trip with tax. That's amazing for peak summer travel, but only specific dates are available. If you don't know how to do a flexible date search for airfare, start here.
 
But if you can wait to travel in the fall, fares are even lower, and in most cases the sweet spot is departing October 23-30, although on some routes you can travel between October 23 until the end of March 2012.
 
Another oddity: these fares seem to be easier to find on Travelocity and Expedia; some are not showing up on Orbitz or Kayak.
 
Even if you cannot find super cheap fares to Spain, there this Spanair/US Airways combination offers the lowest fares compared to other airlines from virtually every U.S. city served by US Airways. And for a bit more, you can visit other Spanish cities.
 
Here is a sampling of fares to Barcelona and to Madrid
 
If you don’t see fares from your city, be creative. Nothing from New York City? Philadelphia is just a Bolt Bus ride away. Nothing from Washington? Fly from Baltimore. But whatever you do, act fast because fares like these may not last long.