DENVER -- With high gas prices and financial troubles for many airlines, it will be tough this year to find bargain fares for the holiday season. And the later you buy, the more you're likely to pay. So now is the time you want to expand your bargain hunting tools -- and look at several Web sites to find the best deals.

You probably know the usual sites like Expedia, Travelocity and Orbitz. But have you heard of Kayak?

Kayak.com lets you wade through the waters of 100 travel sites, including the sites of major airlines like United and Frontier, as well as the bargain sites such as 800CheapSeats.com.

Sidestep.com is another site you should check out. It bills itself as the traveler's search engine and also searches for travel bargains from more than 100 booking sites.

What's also nice about Sidestep is that you can see how your airfare differs, depending on what time you leave, how many stops you make and which airline and airport you use. (If the difference between taking a 5 a.m. flight and a 5 p.m. flight is only $8, would you really want to wake up at 3 a.m.?)

Mobissimo is another useful site to bookmark. It searches travel sites on the Web and takes you directly to the site selling the ticket so you can avoid the booking fees. You don't actually purchase tickets on the site.

What's interesting is that all three search engines have different results for the same query because they use different technology to search and sometimes different "corporate partners." Considering that, it's not a bad idea to try all of them, including the big three -- Expedia, Travelocity and Orbitz.

No matter what site you use, expect to pay more this year than you did last year. To find the best deals, be flexible about your travel dates and times and think about flying to secondary airports.

Other sites you might want to check out:

FareCompare.com

CheapTickets.com

BestFares.com

Priceline.com (really best for hotels)