To celebrate 40 years in business, Southwest Airlines is discounting flights all over the country, with one-way fares of $40, $80, and $120. The $40 flights are shorter-haul routes such as Boston-Baltimore and Denver-Salt Lake City, while mid-range flights like Nashville-Austin and San Diego-Seattle are $80, and the longest journeys (Albany-Las Vegas, Newark-Los Angeles, Philadelphia-Phoenix) cost $120. Tickets must be purchased by June 23, for travel all days except Friday and Sunday from August 23 to November 16. A few blackout dates apply.