I always get questions asking for the best websites to find cheap flights. I know that everyone is hoping there's a magic site that they haven't heard about yet that will have all of the cheapest flights in one place (me too). Unfortunately, that's not the case. Finding flight deals is hard work and unfortunately, there's no magic site. I usually spend quite a bit of time searching multiple websites before I make any decisions. Below are some sites that I like to use when planning both US-based travel and international travel.
Fare Matrix by ITA
The Fare Matrix by ITA software can be used for both US and international flights. It's a powerful flight search tool that is often used by professionals like travel agents to find the best flight deals for a given routing. With the Fare Matrix, you can also set a starting point and and end point, choose a length of stay and set the system to search +/- two days and it will spit out the cheapest dates to buy your flight on. When you're getting ready to drop $1000+ on an international flight, it's a great idea to check the Fare Matrix and see if you can get a cheaper flight by flying out on Thursday instead of Saturday.
If you would like any additional information on how to best take advantage of Fare Matrix's features, check out this guide from The Flight Deal and also this post from Hack My Trip.
Just a twenty-something with a full-time job and a full-time obsession with traveling. It's best to LiveTraveled.