Sister site to The Flight Deal, Fare Deal Alert has the same standard for all of its flight deals – they must be under 6 cents a mile.  Again, it’s totally free AND you can set daily email alerts for the city of your choosing.  Flights are displayed only if they are under 6 cents a mile.  Put more simply, the flights shown are some of the cheapest that you’ll find.  Another one of the world’s top 5 resources for finding cheap airfare.