This app was mentioned in 4 comments, with an average of 2.25 upvotes
I am a huge fan of Skyscanner, especially if you travel a lot. I've found some great prices on flights to see family in normally slow travel times, and plus it's fun to check the lowest prices on international flights to daydream of traveling the world.
Skyscanner for international flights hotels and car rental https://play.google.com/store/apps/details?id=net.skyscanner.android.main&hl=en