If you like, you can specify departure times, a price range, and a limit to the flight's duration. If your flight requires a change of planes, you can pick cities where you'd like to connect. That's handy in the winter when you might want to avoid airports, like Denver, that often suffer delays that time of year.

There's a neat feature -- technically you'd call it a scatter graph -- which shows flights as dots along an X-axis that relates to prices, and a Y-axis keyed to flight duration. By dragging a corner of a box with your mouse (or finger if you're using a tablet) you can change both parameters and only flights that fit within them will be displayed.

Kayak features a slider on its start page that allows you to limit the duration of a trip, including layovers, but you can't combine it with flight prices. On the other hand, Kayak allows you to filter for flights that have Wi-Fi, and as I mentioned, select a particular class of travel.

I set up my search for Chicago flights similarly on both sites: I want to leave on October 17 and return on October 22 and I set the departure times on both the outbound and returns legs for a range of 8 am to 8 pm.