I have an Aunt who gives me all her old wine boxes to upcycle. These are the boxes that you are given when you buy 6 bottles of the same wine. You should be able to get them from most wine merchants.
Last time I made my son a cool nightstand out of the wine box (see it here).
This time I decided to combine the wine box with some LED lights from IKEA to make a light box sign.
The best thing about this lightbox is that I made it so that you can really easily change the signs to whatever you want.