Or if you are looking for a Disney trip rental, check out the Transportation board here on DIS. There is generally a thread for each month of the year with the best codes for that month at all of the major players. Can also check out Rental Car Momma for possible codes.
And of course don't forget about Costco if you have a membership.
But above all else, keep looking for deals, even if you've got a rental lined up. Most bookings can be cancelled so if you find a better deal, go for it.