Good through June 30, 2013, you can get a free 2-day weekend rental from Avis by inputting the following code in the Coupon field:
TUEA002
It requires at least a Friday night. Many locations are showing as unavailable so get on it fast. There is almost no risk since you can cancel your reservation later. I don’t really have a need for a weekend rental between now and then, but I did pick up a rental just for fun this weekend. Full size Impala or similar for $7.60 for 2 days! If you rent from a non-airport facility it will be even cheaper. Have fun!