In the Gujarat where my family are from, the festival honours Lakshmi, the goddess of wealth - new businesses are also started at this auspicious time. Diya's or lamps are lit in every household so that the Goddess Lakshmi will find her way to each house to give her blessings. Another reason to celebrate is the return of Lord Ram and his wife Sita from an exile of 14 years. You can read more about Diwali here.
I haven't made any specific cards this year but I think my Gelli print OM designs can be made into cards and are suitable for the occasion. I know many of the commercial cards depict images of the gods and goddesses and some of my family have mentioned that they would prefer to get something a little bit different.
These are the original Gelli prints and below are the 2 cards I made by printing onto mat photo paper.