How many styles of element separators has LEGO produced?
Bricklink lists two:

OLD: http://www.bricklink.com/catalogItem.asp?P=6007

NEW: http://www.bricklink.com/catalogItem.asp?P=96874

There is one other 'separator', but it doesn't look like it's very good for bricks: http://www.bricklink.com/catalogItem.asp?P=x1220

ETA: The Clickits Separator! http://www.bricklink.com/catalogItem.asp?P=clikits021