I must say, for renting a car, the last week before leaving can be kinda fun. After months of rates starting high and staying high, they finally come down. Not as much as I'd like, but...
Anyway, I've done 5 reservations over the past two days (3 with Hertz, 2 Alamo) for my trip starting the 15th and each time the price has come down...Hertz twice today. Where I am now: Hertz midsize, 8/15-20, AAA discount, $5/day additional off (PC 204358). I'm at 130.40 base, 162.25 total. (Could have done a full size for about $8 more, but don't really need it). A week ago I was at $203 and started at $279 back in Feb. Sometimes the changes are only a couple dollars, but its a couple french fries at Disney.
As I mentioned before, consider Hertz if you have the proper discounts (like AAA). They seem to stay very high until about 8-10 days before leaving. I rented with them in March and it was very easy (do sign up for their free gold club though so you can skip the counter...I've read reports that you need to go to the counter the first time, but at least in March I didn't have to)