What are the cheapest times to fly?

Generally, the airline tickets are cheapest on Tuesdays, but prices are also low on Wednesdays or Thursdays. The prices are lowest at odd hours, such as early in the morning or late at night.

If you are looking for cheaper flights, when you search for airline tickets, indicate that your dates are flexible.

On domestic or shorter flights to hubs, the prices are generally higher in the morning and in the afternoon, and cheaper at noon and later in the evening. This is because of that most business travelers are flying in the morning and in the afternoon.

Because of the predominance of business travelers, Mondays and Fridays are generally considered the more expensive days to fly. Mid-week tickets, Tue-Thu are mostly cheaper, but any differences may depend on route and how far in advance you make the booking.

The lowest frequency of domestic flights are from late Friday night until Sunday at noon.
According to wiki.answers.com, plane tickets are the cheapest during the early part of the week.
Monday night is when most air fare discounts are launched.

Tuesday is the day people purchase the most airline tickets. Wednesday is also a good day to buy airline tickets but by the Thursday and Fridays most of the tickets are sold.