Dirt cheap airfare, absolutely no frills (not even a bag of peanuts tossed in your lap) non-stop flights to small markets around the US. My folks have used them for years out of Las Vegas and swear by them for being cheap and on time. The challenge is that an Allegiant flight to a given destination is on only a couple of days a week. You have to be flexible with your timing to take advantage of the cheap fares.
For kicks and giggles I ran a quick fare check to Branson/Springfield MO. I came up with a fare of 238 round trip. The best fare to a major airport was $308 but would have required renting a car and driving the final 4 hours to Branson. A nice savings in terms of fare and time.
Allegiant Air isn’t for everyone, but for those of us having a need to be in some of the smaller markets it will be a huge savings in fares and time.