Ok, I know this isn't the right forum, but it's an urgent matter because this sale only lasts until 11:59 European continental time tonight - Vueling, Spain's low-cost airline - is giving the return half of any round trip booked with them for free.
Their prices are usually crazy low to begin with (used 'em last time I was there), so it's a pretty good deal. For instance, Amsterdam to Barcelona on a roundtrip comes out to €48 (taxes & fees inclusive) for one of the dates I looked up - crazy, eh?
Get on it!
http://www.vueling.com/EN/latest/offer_happy.php