Travel Deals
If you are a frequent flyer or are often looking for great deals on travel, there are a few good services that let you subscribe and get updates on current travel deals.
Many airfare websites mentioned above offer personalized travel deal updates by email and/or RSS, often by airport or favorite destination. Results are sometimes mixed and are often based on your location - many are nothing more than an automated flight price updates (and not necessarily "cheap travel deals").
Travelzoo Top 20 is a weekly email alert that includes some of the best handpicked travel deals available during any given week. Often these offers sell out fast, so it's a good idea to subscribe and check your email every Wednesday.

Sidestep allows you to subscribe to either domestic or international flight deals via RSS. They also have a Toolbar that you can download to automatically get notified about travel deals, but we have not tested this feature - user reviews are generally mixed about whether or not the toolbar is useful.

After running a search on Orbitz, you can signup for a service that will notify you once a flight that meets your target price becomes available. While in practice it doesn't always perform as well as in theory, it's still a pretty good option if you have some time to book your flight and are willing to wait.

"Southwest Ding!" is a downloadable application that places an icon in your taskbar and notifies you of special travel deals by playing a "Ding" sound anytime a special flight deal is released (usually for a limited time). Much like the Sidestep toolbar, some people find it useful while others find it rather annoying. Results tend to vary according to your location.

(More airfare booking tips below)
Using One Way Flights
Southwest and Jetblue list separate prices for each leg of the flight. If you find that one of the legs of the flight is way is cheaper than the other, check the more expensive route via Orbitz and Travelocity as a one way fare. This way you can book two separate flights using two separate sites and get the best deal on each one way flight.
If you do book this way, make sure that each search was run within the last 10-15 minutes and book them close to the same time. You don’t want to take the chance that one reservation expires before you get a chance to book them both.
Multiple Cities
If you need to book a flight to multiple cities, there are several strategies you can take. Most booking engines allow you to search flights using a “multi-city” or “3-way” option. You should try this first to get a baseline of prices.
It’s also a good idea to break up the flight and run searches for one-way flights for each leg. Jetblue and Southwest treat all their flights as one-ways (even if you’re booking round trip), so they often have good prices for one-way tickets. Orbitz also tends to return cheap one-way flights.
Travel Tips
If you book a round trip ticket with an airline and do not make your first flight, you need to notify them if you intend to use the second half of the flight. Otherwise, they will cancel your entire ticket.
Keep in mind airport parking fees and tolls, which can really add up over a number of days. Use satellite parking when available - it tends to be cheaper. When deciding between airports, keep in mind the cost of gas - and or public transportation / taxi fares.
Some airlines will allow you to change your flight for around $50-100 to a different day if they have availability. So if you want to stay an extra day in New York City, it might only cost you $50 to extend your trip. Call the airline and talk to a customer service rep – they can often be rather accommodating.
If you fly often, sign up for frequent flyer miles with each airline. Even if you book through a booking engine (like Orbitz), you can still apply miles to that particular airline's frequent flyer account. You might also want to look into getting a cradit card (like the Delta Skymiles American Express card) that earn points when you shop - many have double points for things you buy everyday. Those points tend to add up after a while and can be used to get free flights.
If you're a student, check out Student Universe or STA Travel for discounted airfare.

The airline industry is notorious for going out of its way to price discriminate, hike fares, and try to get as much money out of you as possible. Prices fluctuate wildly all the time. However, if you’re a smart shopper and know where to look, you can find cheap flights and avoid being taken advantage of by the dizzying price structures and fluctuations that take place in this industry.
There is no shortage of travel websites out there, and many have redundant searches. At the same time, many sites provide different results. The guide here is an effort to cover a large cross-section of available flights so you can get the best price without having to search 100 different websites. The advice here is based on our own experiences as well as feedback from people like you.