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NEW YORK (CNN/Money) - Search aggregators and supplier Web sites are continually changing the rules of online travel, and staying on top of these trends can help you make the most of your online reservations.

"The major trend that characterizes everything in the travel Internet space is putting more and more current information at the fingertips of consumer," said Charles Buchwalter, vice president of analytics at Nielsen//NetRatings.

A relatively new crop of travel-oriented search engines -- SideStep, Kayak and Yahoo's Farechase are among the most prominent -- act as search aggregators rather than travel agents.

Because they troll through many sites at once, the aggregator search engines cast a wider net than traditional online travel agents, which only run queries against their own database.

The aggregators look for deals from suppliers, travel agents and ticket consolidators as well.

Also, unlike online agent sites you don't book your reservation on the site itself but are linked directly to the supplier.

For instance, if you find a low fare on a Continental flight on Kayak, you are linked directly to the airline's site to book your ticket there.

Because these search-of-search engines offer side-by-side price comparisons, you can look at competing fares without having to make as many clicks.

That reduces the amount of time the consumer has to spend to find the best deal, according to Chicke Fitzgerald, CEO of travel consultancy Solutionz Group.

If you're interested in booking more than airfare, these engines also search the sites of hotels and rental car agencies. Farechase's hotel partners range from EconoLodge to luxury chain Ritz Carlton, while Kayak users can search for cruises and vacation packages as well.

But as travel companies begin to block these engines from their sites, search engines could see their access to information -- the lifeblood of their business -- dry up.

Phil Carpenter, vice president of corporate marketing at SideStep, doesn't foresee that being a problem.

"Some online agents have been slower to come around," he said. "But we think they'll see the value of this and see that it's an important thing to work with it rather than push against."

SideStep partners with Orbitz, but not with Expedia and Travelocity, which means users of its Web site don't get to see price comparisons from two of the industry's biggest online travel agents.

However, SideStep offers a toolbar that users can download and install on their browser. When they travel to non-partner sites, the toolbar which displays the SideStep results stays open so they can see a price comparison in front of them.

These search Web sites take the pain out of searching, but they aren't for every traveler.

"They're a good option for those who are value conscious and are looking for the lowest price," Fitzgerald said. "But for someone who travels a lot, these sites can be a lot of work."

One drawback is that the sites don't allow users to track their purchase history.

For instance, on Priceline, you can create a user account and view your purchase history. But search aggregators don't offer a feature that keeps these these transactions in a central location for you, which can be a hassle if you travel frequently and need to manage multiple reservations.

That may explain why only about 9 percent of online shoppers begin their travel research with these kinds of providers, according to a recent survey conducted by Nielsen//NetRatings.

That survey found that the majority of online shoppers gravitate toward brand name agents like Expedia, Travelocity and Orbitz, which operate as full travel agencies, complete with destination information and customer support agents.

Even though you may tap these agencies for research, that doesn't mean you have to buy from them. You might find a fare offered on Orbitz, for example, then go directly to the airline's Web site and finish the transaction there, thus avoiding the $10 fee Orbitz charges to book a ticket.

In fact, the Neilsen//NetRatings survey found that about half of the people who begin shopping at an agency site end up booking travel directly with the supplier.

"In era where the consumer is being characterized as not being loyal and always looking for the best deal they can find, airlines have done a great thing with loyalty programs, which gives suppliers an advantage," Buchwalter said.

For instance, United Mileage Plus members earn 1,000 extra miles every time they purchase and complete a round-trip ticket on united.com.

Shoppers are also looking for ease of use when they shop, and airlines have been doing a great job converting "lookers" on their sites into "bookers," Buchwalter said.

If you're a Delta platinum member, you can upgrade from economy to coach at the time you book your ticket on the airline's site. But if you book through an online agent such as Travelocity, you have to make a call after you've ticketed your reservation, Fitzgerald from Solutionz Group pointed out.

"It all comes down to whether you want to take that secondary step," she added. "Remember all these sites don't offer the same set of services."

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