The 10 best airfare alert and listing sites

Internet Airfares: Long before there was a Farecast or a Farecompare, there was Internet Airfares, an easy to use if limited site that shows the best fare reductions from various cities. It's not pretty, and only about 50 departure airports in the US and Canada are covered, but it has its charms. Again, no Southwest Airlines and this site doesn't send out email alerts.

Orbitz.com: This well-known online travel agency is best known for its fare search capabilities (like Farecast, it runs on ITA Software). But Orbitz also offers fare alerts with its "Deal Detector" (find it under the heading in the lower left of the home page under "Orbitz deals — delivered to you"). Once there, fill in the departure and arrival airports (you can also opt to get alerts for cities within 80 miles of your main choice), choose whether it's a weekend trip or not, specify your dates of travel, and decide whether you're flexible plus or minus 1 to 3 days. Then set your target price and whether you prefer nonstops. You can only sign up for one deal at a time, and again, Orbitz doesn't list every possible airline.

Sidestep.com: In early September, Sidestep added a unique fare alert product that allows you to track a specific airfare. To use this service, you need to first search for a fare between two cities. Once that's done you'll see the option to track the fare, and you can choose to track either nonstop or connecting/direct flights over a flexible travel date period of between 7 and 30 days in either direction of the dates for which you originally searched, which is a unique feature. Sidestep does not (yet anyway) offer a fare listing service.

Smartertravel.com: This granddaddy of airfare information sites recently added a "deals at a glance" area under the "deals" tab that shows a selection of advertised fare deals. But the site is perhaps best known for its extensive and easily sorted reporting on last minute weekend deals, which are sent out by email or can be seen online.

Travelocity.com: Travelocity, as far as we know, was the first travel agency site to offer a fare watch system. Once upon a time, it tracked both international and domestic fares, but now only covers domestic/Canadian deals. To use it, go to the "Flights" tab and then to "Low Fare Alert" and then click on "Get email alerts" in the upper righthand corner under "Tools". You can sign up for alerts on up to five routes. On the Low Fare Alert page you'll also see a list of fares, from any given city, that have gone down in price from the previous day. Travelocity searches fares just once a day, however, compared to Farecompare's three times a day Monday-Friday.

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Yapta.com: The newest entrant in this burgeoning field. There are two things you can do here: first, if you've already bought a fare, you can enter the flight locator number and then you'll get an alert if the fare has gone down. (Some airlines will refund the entire fare difference in the form of a voucher good for future travel within a year; others deduct $25 to over $300, depending on the fare and route.) But there's also a "Tagger" feature where you can track fares on individual flights, not just routes between two cities.

So, for example, if you really like to take United's morning nonstop between New York and LA, you can track just that flight to see if the price drops to a level you specify, and you'll also get an alert if the price drops between the time you buy and when you fly. Yapta requires that you download an applet, and only works with Internet Explorer 6 or 7, which means it doesn't work on Macs, although a Mac/Firefox version is in the works. And it does not (yet) track fares on all airlines — just 11 so far, and as usual Southwest isn't one of them.

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