RUNNER-UP: AndrewHarper.com
You'll need to pay $200 to join, but the investment is well worth it. Andrew Harper offers a limited selection of world-class domestic and international properties, some at savings of more than 50 percent. On high-end hotels, this can add up to more than $1,000 for a three-night stay.

BOOKING HOTELS IN EUROPE
WINNER: Hotels.com

WHEN TO USE IT: You need a hotel and are particular about the price and location.

WHY WE LIKE IT: Hotels.com, our winner in the U.S. hotel booking category, also comes out on top in Europe. Each time we searched the Web site, it delivered the lowest or second-lowest rate when compared with Euro-hotels.com, HotelsEurope.com, Kayak, and Skoosh. The savings varied widely, but the most impressive deal we found was a room at Rome's luxury Hotel Eden for $609 per night on Hotels.com; it was $788 on Kayak. Perhaps most helpful is the "view by map" feature, which plots hotels and landmarks on a map so you can see precisely how far you'll be staying from, say, the Pantheon.

CAVEAT: Beware the star ratings. Hotels.com rates Paris's Hotel Lutetia as a five-star property, but Expedia and TripAdvisor give it four stars, and TripAdvisor's Traveler Ratings average just 3.5.

TIP: Call the hotel directly to see if it will meet or beat the online rate.

RUNNER-UP: Euro-hotels.com
This Orbitz sister site performed extremely well. Its Member Dollars program can be used for future discounts and for awards bonuses when you refer friends.

BOOKING HOTELS IN ASIA AND THE PACIFIC RIM
WINNER: Kayak.com

WHEN TO USE IT: A good place to begin a search for lodging anywhere in Asia or the Pacific Rim.

WHY WE LIKE IT: The combination of low room rates, terrific search tools, and a wide inventory make for a trifecta. Kayak may be based in Connecticut, but we found that it consistently provided the best rates when we searched for hotel rooms throughout the Asia-Pacific region, although the extent of the savings varied significantly from place to place. In Tokyo, for instance, Kayak's rates were just a few dollars cheaper than the competition's. But when we searched for a four-star property in Melbourne, Kayak's rate of $321 for three nights at a four-star hotel was $84 to $181 less than four other popular sites—Asia-hotels.com, Hotels.com, OctopusTravel.com, and Skoosh.com. It's worth noting that in our experience, Hotels.com, which performed so well when we searched for rates in the United States and Europe, ranked dead last in the Pacific Rim. The best four-star rate it proffered for a 90-day advance booking in Melbourne, for instance, was $502—$40 more than the next-highest competitor.