As has commonly been observed, airline fares are extremely complicated and difficult to predict. They literally change on a constant basis, responding to supply and demand equations built into elaborate computer algorithms that take into account the price of fuel, passenger load, previous years' booking for the same time period, and other factors.
Travel sites like Expedia and surveyors like Kayak give you an edge in finding low fares. The airlines' own sites promise that they offer you the best possible deal on a specified itinerary. But none of these tools can really get you the lowest possible means of going from one destination to another, because the possible combinations of any itinerary--taking into account possible connection cities, stops, class-of-service changes, etc.--are too numerous to analyze.
Enter ITA Software's Fare Shopping Engine, a no-frills tool that appears at first glance to have nothing new to offer versus competing fare-finders and has an unattractive interface at the same time. You have to log in to use it. There aren't any flashy colors. You can't make hotel reservations at the same time. Yet you should take note, because this tool is something special.
The power of ITA's engine is that it allows you to submit queries in route language, a structured code similar to that used by airline mainframes to organize and retrieve their actual real-time data. Any fare-finder will let you ask for a low fare from Washington D.C. to Seattle; ITA can find you the lowest fare from D.C. to Seattle that has exactly one stop going out, at least one coming back, and routes through Chicago. It's also extremely careful to match your preferences, so when you say that you want a morning flight, you will only get morning flights. Period.
ITA's engine doesn't provide for online booking in all cases, because some routes are just too complicated for the airlines' customer-facing Web sites to process. But the software will generate ordering information that you can give to your travel agent or an airline ticket agent in person or over the phone, and you'll get exactly the itinerary and fare code that you saw online.
Does ITA guarantee you the lowest fares? No; it's limited to what it can see, and special rates offered by the airlines on their own Web sites in particular are often restricted from outside viewing to give these sites a "home field" advantage. In the ongoing battle to find low fares, though, there's no doubt that an informed consumer is going to get a better price than one who jumps blindly for the first fare offered.
So, sign up and give ITA a try. It's free, and you just might save a lot of money for the effort.