Frontier Airlines is having a sale for travel Aug. 23 to Nov. 14 on thousands of routes. Frontier says this is a Web only sale, but we found the fares on Travelocity as well as on Frontier's own site.
United and some others are matching some of these fares. Lowest fares, no surprise, are for travel on Tue/Wed/Sat to/from the US and Canada and Mon-Thu for travel to Mexico.
Some of these fares are quite good.