There are no sure things in this city — with one exception: Allegiant Air. While other U.S. airlines have struggled over the past decade from the ups and downs of the economy and the price of jet fuel, Allegiant has been profitable for 10 straight years. The tiny airline focuses on a niche ignored by other airlines: It only flies from small cities to sunny vacation spots. Allegiant entices people who otherwise wouldn't fly with low fares and non-stop flights. Then it aggressively pitches them hotels, rental cars, show tickets and other entertainment, earning millions in commissions.