We just got back yesterday and rented through National after signing up for their Emerald Club through mousesavers.com (it is free through a link there). We used the discount codes there, too. We got our bags, walked across the street to the parking ramp, went to the Emerald Asile, picked out a car (a red Impalla with a HUGE trunk), got in the car, drove to the exit, gave the guy my driver's license and coupon, got the license back and off we went.
Bringing the car back in, drove to the drop off, they had our receipt printed before we got our bags out of the trunk and off we went to the check in stand. Easiest car rental I have ever used!