SecretFlying is my favorite, and fly4free and the flight deal are both solid
Here are some other ones i don't use as much, but might be useful to you
http://www.mightytravels.com/categor...take_fares.php
http://www.flynous.com/
http://www.the-exbir.com/this-is-cur...tremely-cheap/
http://www.dansdeals.com/ (has other stuff, and also paid ads )
http://www.travelzoo.com/uk/cheap-fl...fares-flights/ (just a list of cheap flights, nothing crazy)
Hope this helps!

forgot one!
http://travel-cheaper.de/category/fl...und_fuel_dumps
It's in german, but google translate is your friend.