Priceline.com has a great feature called Name Your Own Price and is a good choice if your travel dat

Traveling by airplane in the United States is very convenient and doesn t have to cost a fortune. Generally, the cheapest fares are those booked as far in advance as possible. Generally prices are the most expensive within two weeks before the departure date.
Priceline.com has a great feature called Name Your Own Price and is a good choice if your travel dates and times are flexible. Here you can bid on round-trip flights and save up to 40% off regular priced fares. This can save a lot of money especially if you re wanting to travel within two weeks of booking your flight.
If you choose to book a flight through Priceline.com, you must be flexible with your departure and arrival times. They may book you at random hours or with a couple of layovers. The money you save on a flight can be worth this inconvenience if you have the time.
Southwest Airlines is a great way to fly within the United States. Their cheapest tickets are in a class called Wanna Get Away. These are usually only available if you purchase tickets through their website. Wanna Get Away fares are non-refundable but if you cancel your flight, Southwest will give you credit for the full amount you paid.
Kayak.com is a website that compares flights from many different airlines. You just enter in the cities you are traveling from and to and the dates you would like and Kayak.com pulls flight information from most major airlines and lists the information for you.