I have accidentally moved a website I would like to keep, into spam, how do I reverse this situation?

Go into the 'spam' folder and check mark the item you wish to keep. Click on the 'Not spam' button and it will be returned to your in box, also allowing that address to be delivered to the in box from now on. However, go in periodically and check to insure all items are spam.

Also, make sure that address is in your address book, as it helps to ensure that address as a "safe" one.