Always innovative and scrappy, Spirit Airlines is offering several promo codes to save you money on their already low fares. You won't find these fares on Kayak, Orbitz, etc and they won't show up in that airfare prediction site, not that you can really predict exactly when airfares will go up or down.
Anyway here's the deal:
Use promo code 24HOURS (all caps) to save $24 roundtrip through Feb 20 midnight ET for travel Feb 21-April 14
Use promo code SAVE48 to get $48 off roundtrip for travel April 15 to Aug 31.
Use promo code SAVE72 to get $72 off roundtrip on fares to or from Los Angeles for travel Sept 1-30.