The proliferation of sites such as Farecast and Yapta is not surprising, travel analysts say, considering that, for the first time, more travel in the U.S. is expected to be booked online this year than by other means, according to PhoCusWright, an Internet research firm. EMarketer estimates that 41.3 million U.S. households will book travel on the Internet, or 52.5% of all households with online access.

It's big business now, and that means the more-familiar online travel agencies such as Expedia.com and Orbitz.com are beginning to face stiff competition. The online travel business generated $80 billion in revenue in 2006. It has increased an average of 28% a year since 2002. By 2010, online travel sales are expected to reach $146 billion annually, EMarketer estimates.

"Things are far more transparent," said Michael Cannizzario, director of information services for PhoCusWright. "There is much more information that is publicly available and accessible."

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