Best Site to Search for Cheapest Airfare

A reporter from the New York Times was asking me some questions about my business model, some how we wound up talking about travel. I told her I was having some problems finding a reasonably priced ticket for a trip we were planning. She suggested I try ita Software's site. It looks like some sort of corporate page ( it sort of is), but you can click on "Search airfares" to begin looking for the cheapest available flights.

ITA Software actually designs the software that other travel sites use like Kayak.com, though unlike Kayak you cannot purchase your ticket via their website. The feature I like the most is the calender view, it will give you all the cheapest flights for any set period of time up to a month out from your start date. This is a great feature if you have some flexibility in your travel plans.