The web is full of fragmented info about special airline ticket deals, there are tens of blogs and forums that publish these offers.
I'd like to round up the most common places people check (forums, communities etc) into a public spreadsheet, so everyone can use them.
Let's leave the ticket search engines a side at the moment and focus on deals that are found by enthusiasts and published on the web.
It might be interesting to you "Hack: VPN and Proxy for Saving Money on Online Booking of Hotels and Airplane Tickets" https://privatoria.net/blog/hack-vpn-and-proxy-for-saving-mo...
Flyertalk forums: http://www.flyertalk.com/forum/index.php
Have had success in the past using Flightfox (http://www.flightfox.com) where you get a 'pro' to find you a cheap flight (for a fee). Have used it twice and both times they found a cheaper flight than I could with the difference being greater than the fee.
Most recently I travelled Melbourne to NYC and they found if I booked an unrelated flight between Manchester and London, the overall cost of the routes I was travelling was much lower, even when paying for an extra ticket I wasn't going to use (though I'm still not entirely sure why)
I also read recently about Skiplagged (https://skiplagged.com/) which finds flights from A - B - C which are cheaper than those simply A - B. If you are only travelling A - B this will be cheaper and you just don't hop on the flight from B - C. They're getting sued by United so obviously someone doesn't like what they're doing.
As for specifically deals, I use OzBargain (http://www.ozbargain.com.au) though this is obviously Australian focused.