This is a great site for finding cheap transportation, including: flights, buses, cars, and even ferries. While they do have tons of domestic flights, they have a global database of 728 airlines (including American Airlines, United Airlines, Lufthansa) and 200 flight booking agencies, which really allow you to find flights in real time and compare them with each other. Check out their app to, for both iOS and Android.
Ever heard of Uber? I am sure you have. This app makes getting around easy. You push a button on your phone, get picked up, and go anywhere you want! Just click the link above to sign up and get your first ride free. I love this transportation app because the gps finds out exactly where you are and you can save locations you frequent.