Through the end of day, Frontier Airlines is offering 25% off all routes. This is for travel December 18, 2015 through January 4, 2016 (blackout dates: December 27, 2015 and January 3, 2016) and you must use promotion code SAVE25.
I am actually surprised to see that almost all of the Christmas / school vacation holiday week is available for the promotion to apply! For those that are looking to book some last minute fares, this might be a good opportunity to save some money.
I personally flew Frontier for the first time a few months back and had a perfect experience. However, for those of you that are looking to bring a lot of luggage (or any luggage at all), make sure to check out the carry on and checked baggage policy for additional fees.