Wikitude – This is a free app that I personally find really useful, both for at home and travel. Basically, the app uses your GPS to find information on places that are close to where you are, be it history, information, pictures etc. A great feature if you are in unfamiliar places.
TripIt – Another free app that allows you to keep all of your travel plans in one place. Use it for your flight itinerary, train tickets, and directions to your hostel. Rather than scrambling to search emails, I love being able to use one app.
Where – A free app that gives you the low down on what is nearby, be it restaurants, convenience stores, gas stations, etc. With this, you will know where all the nearby necessities are location, no matter where you are.
Skyscanner – This free app allows you to search over 600 airlines in a quick and easy manner, and then buy them directly from the airline or travel agent – all from your phone! One feature I really like is that you can email the information to yourself and to groups before you buy, perfect if you are planning a vacation with friends.
Trip Advisor – Just like the site, this app allows you to search for all the best reviews of hotels, food and activities anywhere you are or are traveling to.
GasBuddy – For the road trippers out there in North America, this free app provides the best gas prices in your area. Plan out the route to your destination by hitting up the cheapest gas stations. It also enters you into a chance for weekly gas cards for every station you report.