If you haven't used the metasearch site Kayak in a while, you may like some of the new features that the site has added.
When you search for a fare now, you have a choice of views. Sure, you can still view the traditional list of fares from lowest to highest. But you can also click on the word "matrix" and see a grid of fares ranked by airline. The matrix makes it easy to discover which airline offers the lowest price for nonstop, one-stop, and two-stop flights. (This type of matrix display was pioneered by Orbitz.)
If your dates are flexible, you should click on the word "chart" to see average fares across a period of several days, displayed--surprise!--on a chart. Say you're shopping for a flight from Washington, D.C., to Louisville departing in a few weeks. After you enter the cities and dates at Kayak, a line graph shows the average fares available for that route over about 30 days. This chart hands travelers one more tool to find the best deal online.
Fun factoid: The founder of Kayak, Paul English, is donating his mathematical expertise to the Harvard Medical School in a project to help improve the efficiency of hospitals in Rwanda. He is applying to the problems of medical data the lessons he has learned while fine-tuning fare searches. [Source: Wired.com's Epicenter blog.]