Kayak HD is a free app associated with the popular travel Web site Kayak.com. The Kayak site (whose tagline is "Search one and done") is famous for letting you quickly and simultaneously search multiple other travel sites (such as Priceline, Expedia, and Travelocity), and the iPad app provides similar quick-search options but with some touch-screen innovations that make searching even faster--and even kind of fun.
Fans of the Kayak site will feel right at home with the Kayak app's interface, which has options along the bottom for Flights, Hotels, Cars, and Explore--and in fact, the Cars section is unfortunately indistinguishable from the same section on the Web site. The other three sections are much more interesting, letting you enter, view, filter, and alter itinerary information with simple taps and flick-powered scrolling. It's the same data you enter on the Web site, but the touch screen definitely makes searching easier and faster, and some additional location-aware, touch-specific capabilities--such as browsing for hotels on interactive Google maps, seeing "Hot Searches" from your city in real time, or using sliders to filter for price--can feel downright liberating. One of the most fun features in the app (which is also on Kayak.com, though slightly hidden) is the Explore button, which gives you a world map populated by tiny pins that give the price tag for various vacation possibilities, from a $120 hop to Spokane to a 32-day, $7,730 vacation in Vadodara, India. (Again, a touch slider lets you narrow down possibilities to fit your budget, whether imaginary or real.)
Kayak HD is far from perfect. It's still a little buggy--the Car screen, for example, might come up as a blank white page, and the location awareness isn't always smart (so finding the nearest airport from downtown Seattle will show you Boeing Airfield, which, though technically closer, sees more use from executive jets than economy passengers). Still, the Kayak app is no more frustrating--and, arguably, a good deal less--than navigating most travel sites. If you shop for flights a lot, you'd do well to include Kayak HD in your travel plans.