A number of travel sites, such as Travelocity, Preview Travel, and Expedia to name a few, give you direct access to onlinereservation systems like those used by travel agents. Just enter the dates and times you want to travel, and they'll search for the lowest fares available on regularly scheduled flights. They'll also notify you of any special sales.
Unfortunately, the process can take time,
especially if you have a slow modem. And since the
systems generally require specific dates and times,
you might not learn about all the deals available
to you if you're more flexible.
Keep in mind that even the most big-budget
travel website doesn't guarantee you the lowest
fares possible...just the lowest fares in their
system. Also, you'll find that the search systems
aren't as flexible as, say, a good travel agent:
you can tell an agent "just get me the cheapest
flight leaving the first week of November and
getting back sometime in February; I don't care
when I land at either end." Most online systems, on
the other hand, usually start with the assumption
you not only know your exact travel dates, but the
travel times (give or take an hour).
Take advantage of e-mail services
Several major airlines now have special
services that automatically notify subscribers of
special discounts by email. Besides regular sales,
some companies provide last-minute bargains. For
example, on Tuesday you might find out there's a
special available for the following weekend only.
To sign up, simply go to the airline's homepage
and search. If your itinerary is fixed, or you need
to travel immediately, this option may not work for
you. But at least you'll learn about upcoming
specials on a regular basis.