Alamo offers the AAA discount. They also take entertainment coupons on top of the AAA discount. I always rent with this because of this great double discount. Always ask for the rate first, then say "How about AAA?" When they give you the price then ask "Can I apply a coupon code?" If you have an entertainment book the coupon code are listed on the coupons. I've done this over a dozen times.
I just booked an 8 day minivan rental (Feb) from LAX for $240 (taxes and everything) through enterpirse's 1-800 number with an entertainment book coupon. I orginally booked it via their website for $79 more but dh decided to call and see if he could get a beter rate and he did. I tried all the different rental places online in the entertainment book using their coupons and got quotes ranging from $319-475. I also tried costco's website and they still couldn't beat the $319 from enterprise's website.
You might want to try mousesavers.com. Here's the page http://www.mousesavers.com/rentalcar.html Look on the right hand side and click on respective companies for coupon codes.