Priceline.com

If you don't mind a little uncertainty, Priceline.com can deliver significant travel savings, reports say. However, the catch is that Priceline's best deals are available through blind bidding. You won't know the full details of the flights you've booked or the hotels you've selected until the bids you've placed on them have been accepted and paid for. That said, users still have some control -- you do get to specify a hotel's rating and general neighborhood, and Priceline.com has instituted guarantees that light times, connections and layovers won't be unreasonable. Priceline.com also has a standard booking engine that works just like those at other major travel sites, such as Orbitz.com. If you don't like the idea of bidding, experts say that Kayak.com does the best job of scouring booking sites -- including the company sites of airlines and hotel chains -- to find the best deals.

Although Priceline.com is recommended in quite a few sources, the praise is strictly for the bidding aspects of the site, rather than using it to book travel at published prices. It's included in a recent list of best travel sites at Travel and Leisure magazine as well as in a slightly older list of top travel sites at Kiplinger.com. We found other favorable reviews for Priceline.com at BudgetTravel.com and TriponaDeal.com.