1. Kayak.com
The marketshare leader in travel metasearch engines, many claim Kayak has the best interface of travel search engines, featuring a real-time AJAX search results that is populated as the results are found. Established in January 2004 by the ex-founders of Orbitz, Travelocity, and Expedia, Kayak.com makes money off the advertising on its website.
2. Sidestep.com

The first travel metasearch website, it searches and consolidates results from more than 200 travel websites. Also offers more than 300,000 user-generated reviews and editorial travel guides through partnership with Frommer’s and other providers. Features a downloadable SideStep toolbar for Internet Explorer.


3. Farechase.yahoo.com

Yahoo’s late-comer to the travel search game, the deals found in the results are not as great, and the interface seems to be copied from the others.
4. Farecast.com

The first airfare prediction website. Farecast emerged out of beta on May 15th, 2007. The first and only website to offer predictions on when is the best time to purchase airline tickets. They use over 175 billion airline observations to build algorithms to predict future airline price movements. In May 2007 the company released results of an independent audit verifying Farecast’s prediction accuracy at 74.5 percent and also launched additional features such as Farecast Alerts (a notification service that will inform travelers of key price drops) and a flight quality filter that allows travelers to sort flights by type. In February 2007 Farecast introduced Fare Guard, which allows customers to lock-in a specific price for a flight and be protected from future price increases for the following seven days.






