I found a snake in my yard in Maine, it is white with black diamond patterns on it's back, what type of snake is it? :confused:

As per your description it most probably was a giant marble snake.
You did not provide the snake sizes , so...

;)

Click on Rattlesnakes (http://www.everwonder.com/david/snakes/rattlesnakes.html)

Warning: If you are squeamish about pictures of snakes, this one looks like a bad dude--large, close-up, and threatening!