To root out cheap fares you might otherwise miss, check the website of the airport that you'll be flying into; it will list all the carriers that offer service there, including charter airlines that don't show up in online flight searches. Also, look closely at low-cost carriers, like Spirit Airlines, AirTran and, in Europe, RyanAir, which will usually save you money on the fare — but be prepared to be nickel and dimed for everything else (including hefty fees for checking bags or checking in at the airport instead of online) and don't expect much in the way of customer service.