http://www.spiritair.com/welcome.aspx
Spirit Airlines is having a promotional fare sale...they're calling it Super Tuesday. Anyway, I just booked our flights to Mexico...$99/each way. So, it's $638 round-trip for the two of us together. Last year we flew to Mexico for $88/each way...the price of both of our round trip tickets was STILL cheaper than one round trip ticket with the airline we usually go with.
Not sure if any of you can take advantage of Spirit's offer (it's for travel on Tuesdays only), but if they do fly out of an airport near you it's worth checking out.