Hipmunk is a travel meta search engine.
Kayak is a travel meta search engine.
Google Flights provides a simple user interface to find cheap flights. It allows the user to search and filter flights by destination, dates, cost and a number of other factors.
Skyscanner is a flight search engine that allows users to browse for flights via price and location.
Discover how to get from where you are to where you want to go (plane, train, bus, ferry, and automobile).