SideStep - SideStep was acquired by Kayak, so you'll get the same search results here as you do on Kayak. But SideStep does have a few features that Kayak doesn't: an optional downloadable toolbar that allows you to do easy price comparisons with other travel booking websites, newsletters and travel guides.
Mobissimo - For flights, hotels & car rental.
Farechase - Yahoo's meta-search engine. For flights, hotels & car rental.
Farecompare - This site is powered by Kayak, but it has a different calendar-based interface that some people prefer. In a quick glance, you can easily see how the price to your destination changes from day to day and month to month.
The site also offers great tips on how to travel first-class on the cheap. For flights only.
Vayama - A meta-search engine that specializes in international fares.
cFares - Use their free meta-search engine or upgrade with a $50 platinum membership, which gives you access to unpublished wholesale inventory and instant rebates. According to the site, membership usually pays for itself in 1-2 flights.
This site was Travel & Leisure Magazine's "Best for Airfares" web pick. For flights and hotels.
Inside Trip A fare aggregator for flights that ranks your results according to what's important to you: legroom, on-time stats, aircraft age and type, etc. For flights only.
Online Travel Agencies|
Expedia - For flights, cars, hotels, cruises and vacation packages.
Orbitz - For flights, cars, hotels, cruises, rail and vacation packages.
Travelocity - For flights, cars, hotels, cruises, rail and vacation packages. Also powers Yahoo! Travel.
Cheaptickets.com - For flights, cars, hotels, cruises, rail, vacation packages and events tickets.
Hotwire - Operates two different ways. You can compare rates and book travel with specific hotels, airlines, etc just as you would with Expedia or Orbitz. Or,
you get an even lower rate by booking first and THEN learning the name of the hotel, airline, etc. you'll be using after you make the reservation. For flights, cars, hotels, packages and cruises.
Hotwire is owned by Expedia.
Priceline - Compare rates on specific hotels, airlines, etc. as you would at Expedia or Orbitz or "name your own price" and if your bid is accepted, you'll get even deeper discounts, but you won't find out your hotel/airline/car rental company name until after your bid is accepted.
For flights, cars, hotels and cruises. You can also book airport shuttles and limos, tours and attractions.