Let your computer mouse do the walking and these Web sites—Orbitz, Travelocity, and Expedia—do the heavy lifting in comparing all the going rates at major airlines while you sit back and sip your cocoa
Search engines comb the Web sites of airlines and various budget travel agencies to find the current fares for destinations. Most also throw in hotel booking and car-rental engines.
Using them is usually more of a time-saving technique than one that will get you the absolute lowest price possible, which I almost invariably get by using an aggregator or going to the individual airline's Web sites themselves. Though occasionally I've ended up booking directly through a search engine site (usually for domestic flights, where they seem to be best at pinning down the cheapest options), I find they are best for getting an overview of which airlines service the routes I want and a rough idea of their relative prices.
On occasion, I actually have discovered the absolute best price through a search engine, and since the booking site where that happens most regularly (in my experience) is Orbitz, I've gone ahead and provided a direct booking window for Orbitz on the pages in this site (bottom right corner) to help save you time. Still, I urge you to check them all before buying; you never know.
It should be said that these booking engines sometimes enter into special licensing/promotional agreements with individual airlines. Such agreements lead them periodically to ignore cheaper fares posted by competitors when their own partners are running a special, or result in their refusing to list fares for an airline that won't pay a commission.
In a few cases it's the smaller airlines that have refused to be listed on these Web reseller sites (they've all been accused of one or more of these practices by various airlines, and in fact Congress is currently investigating some of these sites).
Meet the Search Engines
Expedia (www.expedia.com) - Microsoft's foray into travel, a search engine for the discounted fares currently offered by a number of airlines. You'll have to fiddle with the dates a bit (i.e.: putting a day earlier or later and submitting a search again) to find lowest fare. Of all the biggies, I find that Expedia usually manages to return the best fares, especially domestically.
Orbitz (www.orbitz.com) - When the big airlines saw how much business Web sites such as Expedia and Travelocity were doing, they decided they could cut out these middlemen. American, Continental, Delta, Northwest, and United banded together to launch their own site in 2001, though now it's run independently of its founders.
It lists some 40 affiliates, covering many of the world's major airlines, and claims its search engine culls results from more than 445 different airlines. It also boasts a "matrix" search system which allows you to be as fuzzy as you want with departure dates and such and set your own priorities to find the cheapest fare (basically, it shows you on a single page, in a grid, what the price would be going or returning 1-2 days earlier or later).
Travelocity (www.travelocity.com) - In January, 2015, Expedia—which had already been running the search functions of Travelocty for nearly a year—bought the company outright. Whether it will live on as a marketing vehicle remains to be seen, but practically speaking, "Travelocity" is now just another name for Expedia. Previsouly, this was one of the first Big Boys on the Web travel market, an offshoot of that old travel agent's best friend, the Sabre reservations system.