Here's a very flexible idea:
Printing on card would have so many applications, especially if the card could also be cut, bound or laminated. Such cards could be used as business cards, greetings cards, invitations, display signs, party or promotional drink and place mats, flash cards, presentation tools, infants' books and more...
As a game designer, I'm interested in the possibility of selling games as a set of printed cards that can be cut, folded and pasted to make the playing cards, multi-part board, playing pieces and the box to keep it all in. Up until now, I have been offering this as a download-and-print option (expensive for the buyer) or getting sets mass-produced (expensive and time-consuming for me).
Just printed card alone would be very versatile indeed. How about it, Lulu?