"Private Sale" Travel Sites

• SniqueAway.com - limited time discounts on hotels (by invitation only)
• TabletHotels.com - boutique hotels
• JetSetter.com - insider prices on vacations

Fitness

• IdeaFit.com/fitness-boot-camps - find a fitness boot camp near you

Other Travel Sites

• Zicasso.com - specialty travel companies
• Translate.Google.com - use on web-enabled phone while traveling
• XE.com - currency exchange calculator
• MapQuest.com - can add custom resources (gas stations, restaurants, etc) to your maps
• Maps.Google.com/streetview - quick look at where you're going before you get there
• HopStop.com - directions for public transportation in major tourist areas
• WebFlyer.com - maximize your frequent-flier miles
• BestParking.com - search for cheap, off-airport parking
• PromotionalCodes.com - look for discount codes under "Travel"
• CouponWinner.com - look for discount codes under "Travel"

Cruises

• VacationsToGo.com - offers extras passed on by cruise lines to the biggest booking agents
• CruisesOnly.com - booking site
• CruiseStar.com - booking site
• CruiseBrothers.com - booking site
• Cruise.com - booking site
• OnlineVacationCenter.com - booking site
• CruiseCritic.com - cruise reviews
• PortCompass.com - alternative shore excursions
• ShoreTrips.com - alternative shore excursions

Home Rentals

• HomeAway.com - contact owners directly and negotiate price
• VRBO.com - alternative to above
• Zonder.com - another alternative
• Rentalo.com - similar site to the above
• SecondPorch.com - similar to above but with social networking features
• AirBNB.com - room rentals

Hotels

• HotelsCombines.com - searches obscure discounters in addition to the major players
• GetARoom.com - blind bidding similar to Priceline and Hotwire
• BetterBidding.com - advice from travelers on Priceline/Hotwire/etc bidding
• BiddingForTravel.com - advice from travelers on Priceline/Hotwire/etc bidding

Car Rentals

• AutoSlash.com - also alerts you if rates drop after you've booked
• BreezeNet.com - includes local, smaller companies also

Airfare

• Kayak.com - supports multi-hop itineraries
• Fly.com - meta site
• FareCompare.com - meta site
• AirfareWatchdog.com - manual searches by actual people
• Momondo.com - Leaves no stone unturned (includes high-speed European train routes)
• Dohop.com - broad, impartial search
• Bing.com - price predictor
• STATravel.com - for students
• StudentUniverse.com - for students
• Hipmunk.com - sorts according to "agony" index (price, length of flight, number of connections, etc)
• InsideTrip.com - evaluates by legroom, aircraft age, on-time performance, etc
• Yapta.com - alerts you if rates dropped after you've booked