Kayak was started in January, 2004, by several of the original founders of Orbitz, Travelocity, and Expedia, and it has raised $30 million to date. On May 22, it's set to announce yet another round of funding. Kayak is using the money to develop features, such as social networking applications that could help you better plan trips with friends and share vacation photos. And in good old 1999 dot-com style, it's also launching a marketing blitz.

Like SideStep, Kayak does an outstanding job of ordering up scads of low airfares in seconds. It took less than a minute to come up with more than 800 early June flights from San Francisco to New York, from rivals like Cheaptickets.com to the airlines themselves (who knew Alaska Air (ALK) traveled that route?). They're served up starting with the cheapest ($295) to the most expensive ($970), but you can rearrange results just about any way, narrowing the price range, eliminating certain airlines, reducing the number of stops – you name it. Kayak does that by using a programming technology known as Ajax, which is designed to make a faster, more interactive Web site.

But as good as Kayak is, I found it didn't consistently dig out the cheapest fares. And Kayak lacks the toolbar I found so helpful on SideStep. Once downloaded, it automatically pops up and starts scouring its own inventory every time you log a search on a competing travel site -- no reentering data, no flipping between windows or taking notes. Kayak Chief Executive Steve Hafner sniffs that SideStep's tool is little more than glorified spyware. You know what? I don't care. It lessens my travel-planning headaches and I love it.

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