I just helped friends who will be staying with us this summer find their tickets.
The military discount tickets from Shades of Green were by far the cheapest. If you're military, retired military, or DoD civil servant, this is the way to go. One person in your room can sponsor buying tickets for the whole room, so you don't all need to have military ID cards.
The next best deal I found was from UndercoverTourist.com. They beat the AAA prices by a few bucks. There's also a discount from the Kissimmee Wal-Mart, but it wasn't as good as the others I checked.