Frontier
Based out of Denver International Airport, Frontier Airlines is a budget carrier that offers flights to 29 states within the U.S., as well as a handful of international routes to the Caribbean and Mexico. With 55 destinations in total, Frontier is an emerging force within America's low-cost carriers, with their fleet of 59 planes set to double by 2016. Frontier currently operates a code-sharing agreement with Great Lakes Airlines that allows easier connections through their primary hub.