Yes, Travelocity.com (I use the Yahoo-branded version
) shows the lowest fares on the books for
the trips you want to take, if you check the box saying My dates are
flexible, although you need to check one airline at a time. Orbitz
has some flexible date options for trips
within the U.S. and Canada. You can say I'd like to take a weekend
trip in October or I'd like to take a trip of 3-5 days between Oct.
1 and 15. None of these sites include Southwest, if they fly your
route; the airline's site just this week
started having a Shortcut to low fares feature that lets you see on
a calendar when the lowest fare is available.