
I travel for a living. I also do quite a bit of travel for pleasure too. I have the benefit of using a corporate travel agent when booking travel for work. However, when I travel for pleasure I'm on my own. Sure I've used travel sites like Travelocity and Orbitz. I've used Hotels.com and direct booking booking with airlines and hotel sites. Many of these travel sites have Apps and I've used those too. However, I haven't found an App that can handle all types of booking and one stop shopping like Kayak Pro can. While there are some good Apps out there, Kayak Pro has the best UI that I've seen to date and can take you all the way through the process of not only searching for deals but booking them too. You can book your Flight, Hotel and Rental Car all from within the App. It searches multiple carriers and deals and even lets you make the ultimate choice of which site you book it through.
It's all about the UI

Kayak Pro impresses me most by having a very clean and easy to use user interface. Tap the appropriate form of transportation such as a plane, bed or car and then you're presented with a screen asking for the location you want to travel to/from as well as the dates. Once you hit go, your results will be listed by order of Cheapest first. You can change the sort order to something like "Shortest duration", which would give you non-stop flights first over connecting flights. You can then just tap the deal you want to proceed with the booking. Since Kayak Pro searches the deals of the other travel sites such as Orbitz, CheapTickets.com, etc. it truly is one-stop-shopping.
Auto-Fill Rocks
Since Kayak Pro can offer booking on any one of a number of sites, it would be tedious having to enter your information in every time you want to do a booking. Therefore, Kayak Pro offers an optional "Auto-Fill" feature where you key in your information such as name, address, phone number etc. once in the App and then it can auto-fill this information for any bookings you make within the App. I used it to book a hotel and every screen that came up within the App asking for my info was already filled in with the exception of the Credit Card info, which the App doesn't offer.
It's Great, but it Could Be Better
The App works great at booking your Flight, Hotel and Car Rentals, but what about trains? There are no rail options. Also it would be nice to have it search for Flights, Hotels and Car Rentals all at the same time as an option as well as booking the whole trip at once.
The Bottom Line
The Kayak Pro App is now my default App for searching for and booking travel deals for my personal trips. While I do use FlightTrack Pro and TripIt, it does have both a flight tracker and "My Trips" function as well to monitor the trips that you book.
It's a Universal App for iPhone, iPad and iPod touch
You can get Kayak Pro for $0.99 here from the 
You can get the FREE Kayak version that has Ads here from the 