Bing Price Predictor - Should you buy that airplane ticket now or wait? The Bing Airfare Price Predictor tells you whether airfares are above or below average now and whether they should be coming down in price soon.

Kayak - Search for flights, hotels and car rentals across all the major sites at once to help make sure you always get the best price. This app also can store your itineraries and alert you if fares go down.

TripIt - This free app organizes your itineraries and loyalty programs in one place. A pro account $49/year gets you alerts for flight delays and cancelations, and potential ticket refunds if the airfare on your flights go down. Many people don't know that some airlines will refund the difference if your ticket price goes down. TripIt helps you take advantage of these deals.

Hotwire - Hotwire always has the best prices on car rentals. You can also set up a Travel Ticker Alert to tell you when prices on flights, hotels and car rentals on your watched routes or destinations have dropped.

Homeaway - I think renting a house or apartment is much more comfortable that staying in a hotel if you are traveling with kids. I like HomeAway for house rentals because the listings always have lots of photos and you can filter your results by the amenities your need like pet friendly, internet access or waterfront.

HomeExchange - There's no app for HomeExchange, unfortunately, but I still need to mention it. I love house swapping as an affordable way to vacation with a family. Read more about house swapping here.