National and Alamo both are on property at the car care center in the magic kingdom parking lot. If you call them, they will come pick you up and take you to the center to get the car. I think they may also have a booth at the Swan or Dolphin.
We rent our car through Avis which is located in the Hilton hotel across the street from DTD. We find this convenient. We'll check in and grab the keys and walk back over to DTD to spend the rest of the night. When we're ready to go back to the resort, we'll walk back over to avis and grab the car. Returning it is pretty convenient too. We'll drop it off in the morning and grab some breakfast sandwiches from Earls before grabbing a bus back to the resort.
There is a sticky thread at the top of this forum that the OP should read. It has a list of all the rental agencies on property. Be sure to shop each of them for the best rate.
Thank you all for the great help i have been going to disney every year for 10 yrs now and never needed a car untill this trip coming up thank you all so much