If you are talking about the theme parks, no ther eare no advance parking passes. But parking is free if you are staying on-site.
As for entering the parking lot, you will be directed by Disney CMs. Parking is very orderly and you will likely park in between the person who enters right before you and the person who enters right after you.
I don't believe that you can buy parking passes in advance. You just pay the $8 or whatever as you enter the parking area. As far as getting a close parking spot....Get there EARLY!!
I don't believe there is any kind of discount for parking. It is now $9.00 a day but you only pay once. Keep your receipt if you leave and drive to another Disney park so you won't have to pay again that day.
There is no charge for parking for guests of Disney resorts.
To the original poster......the lots at all WDW parks get pretty crowded. You will likely have to take the tram to the park entrance. For the Magic Kingdom you park at the Transportation and Ticket Center. Then tram/or walk to either the boat or monorail to the MK. If you are staying at a Disney resort the Disney buses drop off near the MK entrance. No other vehicles are allowed near the MK entrance. Just one more tip....make sure you note the location where you parked. The lots are HUGE and it can be difficult to find your car later if you don't make note of where you parked.
As someone else said, the only way to get a close up spot is to arrive EARLY. Most frequently you will have to take a Tram to and from your car to the entrance of the park.
Re:AAA, I believe you get Diamond Parking passes when you book through AAA for your trip. That gets you very close. Some have said their AAA will give them a pass without arranging the trip through AAA, but it seems to vary by location.
We had the AAA Diamond pass last trip. It was so worth it! As my DH said, it really makes you feel special to get to park in those special spots. We got it for booking through AAA. I hate those tram things so not having to ride them made the trip. As others have said, there is no parking discount for AAA. Unless you are staying at the resorts, you are paying the same amount as everyone else.