When it comes to airline headaches, the realization that the guy next to you paid a lot less for his seat is right up there with annoyances like missed connections and lost luggage.

Most people might chalk it up to the unfathomable mysteries of airline ticket pricing and move on. But not Oren Etzioni.

On a flight from Seattle to Los Angeles a few years ago, Etzioni learned that an aisle mate had paid about $100 less for his ticket than Etzioni had.

When he returned to the University of Washington, where he is an expert on artificial intelligence, Etzioni set about creating a computer program that could ensure that fliers get the best deal.

His brainchild, Farecast.com, attempts to tell travelers when they should buy a ticket, predicting whether a fare will go up or down.

"It was a very personal thing for me," said Etzioni, who still teaches at the university and is working on other "intelligent" Internet search engines. "I was frustrated and I thought to myself, this is terrible and it needs to be solved."

Farecast has created a lot of buzz in the travel industry, but it's just one of a bevy of Internet-based travel services and tools that are redefining how travelers book flights.

"The online travel market is a hotbed for experimentation," said Jeffrey Grau, senior analyst for Internet research firm EMarketer. "New travel sites are seemingly popping up weekly."

A few weeks ago, a new site, Yapta.com, made a splash by launching a tool that can "tag" specific flights and alert a traveler when the fare changes. Yapta is an acronym for "your amazing personal travel assistant."

One advantage of the service is that if the fare drops after it has been purchased, the traveler can typically request a credit voucher or a refund from the airline. The catch: To qualify for the credit, the ticket must have been purchased directly from the airline.

The proliferation of sites such as 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.

The fast-growing industry should be good news for consumers, analysts say.

"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."

So how can consumers navigate through the Internet maze to get the best deals?

First, expect to stay glued to the computer as you comparison-shop. Half an hour of browsing could save you a lot of money. You might also end up where you began, but without doing the research you'll never know whether you could have gotten a better deal.

Frequent travelers typically consult at least three different types of websites: the direct providers (the airlines themselves), the online travel agencies and travel search engines.

Some veteran travelers start by checking fares on their favorite airlines, which often offer online specials.

Next, they'll query the "Big Three" online agencies — Expedia.com, Orbitz.com and Travelocity.com — to see whether they can get a better deal.