Kayak.com

Reviewers and users agree that Kayak.com is the best resource for finding the cheapest air, hotel, cruise and car-rental prices. Sites such as Travelocity.com and Hotwire.com search only their own databases, but Kayak.com includes more than 400 airline websites, online travel agencies and other travel sites, including some international ones, in its search for the best fares and fees. One interesting tool lets you see the best fares for similar routes searched by other Kayak.com visitors; you can also receive fare alerts and compare search results to other travel sites like Expedia.com. There are no booking fees. Keep in mind, though, that reviewers say Hotwire.com is better for finding discount hotel rates, while Priceline.com's bidding model can deliver cheaper airfares as well as hotels. The caveat to both, however, is that you won't know exactly where you are staying, or even the exact time you are flying, until after your reservation is paid for.

We found lots of expert feedback regarding Kayak.com. The best reviews can be found at Kiplinger's Personal Finance, PC World magazine and The Washington Post. Each of those reviewers compare Kayak.com to other travel sites for efficiency at booking the lowest rates and prices.