Also, remember that, on the Signature card, you get double points for all AirTran spending.

I just bought $500 of gift certificates on my card - this will earn me 5 credits due to the gift certificate program in force until February, plus 1000 points on the Visa which converts to one more credit. Then add in the credits I will earn for the flights I have booked using my gift certificates, and I will easily have earned a free one-way from just $500 in spending!