Shopping online for airline tickets used to be a no-brainer. All you needed was a few minutes to browse the "big three" -- Orbitz, Travelocity and Expedia -- and voilá, you had your ideal itinerary at a sensible price point.

While buying tickets online is still the most efficient way to book a flight, the online travel landscape is getting increasingly harder to navigate. Not only is there an abundance of seemingly similar travel sites and search engines to pick from, but tickets are also becoming less and less affordable.

"We have been spoiled by absurdly cheap air fares in the past," says Henry Harteveldt, vice president and principal analyst with Forrester Research, a company that follows travel trends. "As much as it's a shock to see prices go up, we see how much it costs to fill up our own gas tanks. So, we can only imagine how much the airlines must spend on jet fuel."

Still, high prices are hard to reconcile, especially for bargain-hunting travelers. There are deals out there -- they're just harder to find.

"The key to getting a deal is to be a flexible shopper," Harteveldt says. "Consumers need to do research and explore nontraditional ways to get to their destination."

That means browsing -- not just the big three, but also the slew of relatively new travel search engines, such as Kayak and Mobissimo, as well as the increasingly popular sites that combine travel planning with community, such as TripAdvisor and newbie TripConnect. You may not be able to actually book flights directly from these sites, but you'll get great feedback on how to best plan your trip and find the best air deals.

"The big three online agencies have totally redefined how we buy and sell travel," he says. "But there's certainly room for more innovations." In fact, most travel experts welcome these new sites. They urge travelers to take the time to explore their options and shop around. That doesn't mean you need to spend hours scouring the Web, but you shouldn't be too impulsive because fares fluctuate.

"As much as we'd love to find that one-stop shop travel site, it just doesn't exist. There is no one site that can possibly capture all of the available airfares," says Bill McGee, a consultant for Consumer Reports WebWatch, a project of Consumers Union. "Because each third-party site negotiates rates and fares in proprietary ways and at different moments, it's hard to get a snapshot of what's available in real time."

Sometimes, of course, you will stumble upon a great deal early on in the shopping process. In that case, experts say you should take advantage of it before someone else does. "There are fewer lower fares out there now," says Joel Frey, a spokesman for Travelocity. "So, if you see a deal, don't hesitate to book it. It could be gone in a half an hour."