www.kayak.com
It searches all the airline companies & airports closest to your desired airport to find you the best deal and then redirects you to the airlines website so you can buy it directly from them thus saving yourself the $10-30 fee Orbitz, Travelocity, etc charge you. Very rarely do I buy from the travel sites only because it will be cheaper for you to buy it directly from the airlines website plus if you have their frequent flyer card you normally get 1000 bonus miles or so for purchasing from their website.
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