If you travel in Asia, or plan to, then may I suggest subscribing to the Airasia Newsletter. AirAsia are the largest low cost airline in Asia and they often have some amazing sales.
An example of an AirAsia promotional email.
Since I have been subscribed to the newsletter I have picked up some ridiculous bargains, such as:
Kuala Lumpur to Melbourne for 234 MYR ($75 USD)
Kuala Lumpur to Delhi for 60 MYR ($19 USD)
The flight to Delhi was free plus tax, and $10 of that was for checking a bag.
AirAsia fly all over Southeast Asia, China and India as well as Australia and the UK, so there are plenty of travel options. Even if I am not travelling to Asia for some time, it just makes me happy getting offers to go to places like Padang, Penang and Phnom Penh.