Along with the ''Big Three'' and the metasearch sites, check out these:
www.yapta.com: Alerts you when the fare drops for a ticket you've already purchased, so you can request a refund. Drawback: Includes only 10 airlines.
www.seatguru.com: Check out airline seat positions before you choose
www.flyertalk.com: Online community for frequent flyers
www.airtreks.com: Ticket source for round-the-world flights and unusual itineraries
www.bestfares.com: Membership site ($59.90 per year) finds deals on all kinds of travel
www.airfarewatchdog.com: News and deals hand-picked by a savvy editorial staff. www.farecompare.com: Booking site with many cool features, including first-class ticket deals and handy deal-driven getaway maps
www.farecast.com: Helps you figure out the cheapest times to buy
www.skyscanner.com: Cheap flights globally, but with limited destinations from the U.S. Best for point-to-point flights abroad.
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