The Skyscanner Flights Live Prices Curl Sample Code demonstrates how to implement flight live prices in a travel application. Details include country, currency, locale, origin place, destination place, inbound and outbound date, and number of adults, children, and infants.
Travel reservation site Expedia starting working on its Expedia API back in 2009, according to the changelog. It has three APIs, covering hotels, flights and cars. Don't be shy. Expedia has been expecting you. The Expedia developer site has all the warmth and care of a fine bed and breakfast. They clearly want to invite you in, make you comfortable, and get your development project of the ground. Though they do have a couple hoops to jump through, as well.
Flight price tracker Yapta's value proposition sounds a bit like Robin Hood of the travel industry. It will not only track travel prices for you, but to help you get a refund should the price of your reservation fall after you’ve booked it. I wouldn’t be surprised if Yapta can also be used to retrieve kittens from high branches, but that part of the Yapta API isn’t documented yet.