Kayak.com is an interesting meta-search engine. Kayak itself sells nothing, but what it does do is find airline prices and information. That's something that had been limited to Priceline, Orbitz, etc., and the airline sites.
When you log onto Kayak.com, you are presented with a simple search form that asks where you wish to travel. You can search for one-way or round-trip trips, as well as multi-city itineraries. Clicking the "Search multiple sites" button starts the action.
The results page graphic shows airline websites being scanned for their up-to-the-moment information. Kayak has the ability to go to nearly all of the airline databases, extract their information and reformat it into something understandable. The animated display also shows you an interim status of specific airlines that are being scanned at that moment.
When Kayak is done, you are presented with an ordered list of flights that meet your search criteria. The default is to sort them by price, from the most economical to the very expensive, but can change the sequence as you desire. It has many other cool features and can also help with hotels, cars, etc. A great alternative that is not beholding to any airline.