Indian Gods

Lord Ganesh, the son of Lord Shiva and Paarvati, was blessed by Lord Shiva that he will be worshipped first in all the religious functions and festivities. 

Radha-Krishna in a Lotus Pond.

Kali, the goddess of transformation (or so the back of the card says).

Postcards sent by Amita (India) and Phillip (the USA).

Diwali

I think that in USPS you can find a stamp for every celebration, like this one for Diwali. 

According to the Wikipedia, it symbolises "the spiritual victory of light over darkness". Certainly, the postal workers needed a big lamp to see this almost invisible address on the envelope!