Through the end of day, Frontier Airlines is offering 35% off all routes. This is for travel December 18, 19, 21, 22, 25, and 31 and you must use promotion code SAVE35.
While dates are extremely limited, if you are looking for a last minute vacation, this sale could help you out quite a bit! For example, a flight for this Friday evening from New York to Miami (which is a PEAK travel day) is only $119 after the promotion is applied.
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.