Mirror the list of one board on another
Magic Mirror List for Trello allows you to mirror the list of one board on another. Furthermore, if you drag a card to the mirrored list it will be transferred to list that it is duplicating (and thus be shown as a copy in the mirror list).
To get started, create a list on a board with a title containing the list and board to mirror, following this syntax: "[My list to duplicate@The board that list is on]".
Obviously you need to be able to access both boards, and allow the plugin to act on your behalf as described in the OAuth dialog.
1.13 Fixes problem with changed styles on Trello