What is the best site to buy cheap plane tickets?

Buying through the airline is almost always the best way to go. Sites like expedia.com or orbitz.com always have exactly the same fares as the airlines but they also tack on a “booking fee” so it’s actually more expensive booking through those sites. (The only thing those sites are good for is comparison shopping to see which airline is cheapest). Also check the “low-fare” airlines such as JetBlue or Southwest Airlines – they only have their fares available on their own websites. Although in my experience those airlines are no cheaper than other airlines.