Skyscanner is a flight search engine that allows users to browse for flights via price and location.
Hipmunk 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.
Kayak is a travel meta search engine.
Discover how to get from where you are to where you want to go (plane, train, bus, ferry, and automobile).
Liligo is a travel search engine allowing users to compare flight, train and bus tickets.