Spirit Airlines is having a sale. Travel June 5 to November 14 and purchase by midnight May 29. This is nothing new. They always have sales. And while the economy class fares in this sale aren't especially amazing, one thing should not be overlooked: if you're a big person, or you don't like sitting in those thinly padded economy class seats (they're getting thinner and thinner, and it makes sense since a thinner, lighter seat saves on jet fuel costs) then you should take a look at Spirit's business class fares in this sale.
Just one example: New York LGA to San Francisco for $398 RT before taxes if you travel Tuesday or Wednesday (slightly more on some days of the week). We searched on Travelocity leaving Monday June 11 returning Sunday June 17 and found a lowest business class fare of $1375 RT on US Airways. Spirit's lowest fare was $499 RT, a huge difference. Spirit's "Big Front Seat" business class doesn't provide meal service or free drinks, so it's not really on par with business class on other airlines. But you do get a comfy seat at the front of the plane, and to our mind that's what counts.
From Spirit's site, LGA to SFO $499 RT
From Travelocity, LGA to SFO $1375 RT. Note that Spirit's business class doesn't even show up.