Mobile App: Find a flight, hotel, or car rental
With its stripped-down interface, Kayak is easy to use, making it our favorite way to look up airfares, as well as hotel rooms and rental cars. For flights, you can sort your results by price, trip length, and even departure and arrival times using Kayak's signature sliders. One hitch: you'll need to upgrade to the Pro version to get first- and business-class fare quotes.
Cost: Free; $1.99 for the Pro version.
Runs On: Android, BlackBerry, iPad, iPhone/iPod Touch, Windows Mobile.
Runners-up: TripAssist by Expedia (free; iPad, iPhone/iPod Touch), Travelocity (free; Android, iPad, iPhone/iPod Touch).