With record flight delays, tightened luggage restrictions and average round-trip fares that top $325, you need to do some serious planning to get the best deal on your next plane trip. But the plethora of travel Web sites often adds noise to the process. So we've whittled your choices to three need-to-know sites.

For both domestic and international fares, Kayak is the place to start. In just a couple of minutes, it will fetch hundreds of airline fares, from Delta to Darwin Airline. You don't book fares through Kayak; instead, it redirects you to the Web site that offers the fare you select. However, it does pass along your search criteria, so all you have to do is confirm the flight details and book your ticket. Kayak doesn't guarantee that you'll get exactly the same fare, so double-check the price before paying up.

As comprehensive as Kayak is, it doesn't list prices for some major discount carriers (notably Southwest) as well as some smaller airlines. Airfarewatchdog.com is the best place to keep an eye on these. It's also usually the first to sniff out the lowest fares offered through unadvertised "fire sales," when airlines try to fill empty seats or promote less-popular routes by dropping fares and posting the discounts on their own sites.

With Airfarewatchdog, you can sign up to receive e-mail alerts on deals from up to five departure airports. But like Kayak, it doesn't book your flight for you — it redirects you and your search criteria to the site where you need to go to close the deal.

There is one exception, however, and it's a big one: Southwest. Despite the airline's won't-play-ball attitude, it's worth the trouble to check with Southwest.com directly. For example, a round-trip flight between San Antonio and Las Vegas recently cost $185 on Southwest, compared with $223 for the cheapest trip on Kayak. You can download a tool that sends you alerts about Southwest fares from up to 10 airports of your choosing.

No matter where you find your flight, be sure to book it with the airline, preferably online. Many online travel agencies charge a fee of $3 to $15. Booking by phone can cost you an additional $5 to $25.

If you get bumped, you'll be glad you bought your ticket from the airline itself. Complaints about overbooked flights jumped 53 percent in 2007 over the previous year, according to the U.S. Department of Transportation. When you buy a ticket directly from the airline, it is more likely to help you get on another flight free. You're also more likely to be offered free-flight vouchers for volunteering to take a later flight.

Stacy Rapacon is a reporter for Kiplinger's Personal Finance magazine. Send your questions and comments to [email protected]