Maybe this has been around for a while, we're not sure, since it's well hidden: the ability to do a flexible date search over any one month period and over a range of length of stays. To get there, click on "advanced options" from the home page. We suspect this is powered by our friends over at ITA software, and of course, it only shows Continental's flights. But if CO is your airline of choice, it's a great tool. Once you see the page below, click on "my dates are flexible"