Randomly Disney World mails out special invitations to guests that have either stayed in a Disney Hotel before or that have registered at the Disney World website.
These invitations will contain a unique code called a pin code. These codes vary on the discount amount but are usually provide a decent discount on vacation packages.
Unfortunately Pin codes are not transferrable and can only be used by the person they were sent to. No one knows the methodology for who they send the discounts to and when they send them but it is a good idea to register at Disney World to see if you receive one these discounts. Registering also gives you access to member only discounts. Register here