Cheap flight ticket search engines

These websites allow searching for a cheap flight ticket among a lot of carriers, mostly in Europe. You just have to specify a time window, origin and destination, and it finds the cheapest offer. http://www.kayak.com/ http://www.orbitz.com/ Even though it saves time, it is better to also check the offers at the websites of the flight companies. Sometimes the offer there is some euro less if you buy directly from them.