Since it seems like this is turning into a general cheap flight tips thread (not that I'm complaining):
This is my usual go-to:
http://www.skyscanner.net If you haven't decided on a date yet, use the "whole month" feature so you can leave on the cheapest date and book your vacation accordingly.
I used to use expedia, but this is often a couple hundred cheaper when I'm looking. I've also had some bad experiences with Expedia that their staff didn't even seem willing to help with.
Also, google "travel-hacking" and there are tons of tips for you to find cheaper flights. But to be honest, some of the things require so much work that I can't justify the headaches that come with it.
Some other things you can do:
- find a cheap flight using a travel aggregator (hotwire, expedia etc.) then go directly to the airline's website to save on the service fee/add-on
- fly to a hub: bangkok, JFK, heathrow, LA, etc. are all hubs with hundreds of flights in every direction. They'll sell off seats cheaper if they can't be filled
- break up your flights. You can actually save hundreds doing this. Sometimes it's at the cost of a longer layover, but it depends on how much time you have. Sometimes a day in another country on the way to your final destination isn't necessarily a bad thing, right? You also don't necessarily even have to have long layovers...sometimes the flight aggregator sites miss certain flights or don't deal with certain airlines. So you just have to book individual flights to connect yourself.
Google "Chris Myden" then subscribe to his e-mail alerts for Toronto, Ottawa and Montreal airports. You'll hear about special offers long before others.
Thanks!