For us, the denizens of the East India, celebrations starts today with the Durga Puja. It is one of the widely celebrated festival across many states in East India. Today is the first day of Durga Puja and is called sasthi. The 10 handed lion riding idol of Devi Durga brandishing 10 different weapons killing the demon Mahisasura will be placed with all respect at the alters of puja pandals. The puja will peak on the day of Asthami and will finally end on the day of Vijaya Dashami on 2nd October with the immersion of devi idol in some water body. The modern day form of Durga puja had probably originated in Bengal but the tradition had spilled over to neighboring states. In my native Assam, it is celebrated with equal pomp and glandour as is done in Kolkata. Want to send e-cards to your friends --- use this free site Happy Durga Puja.
The festival season in India had started last Saturday with the celebration of Navaratri in North and West India, though it is celebrated in entirely different ways in these regions. There may be different ways to celebrate this 10 days of worshiping, but it all had probably same mythological origin. It symbolises the power of female form and victory of good over evil.
If you are not from India, what may interest you is the Durga Puja celebrations in Kolkata (28 to 2nd Oct) and the Dusserah celebrations in North (2nd Oct). If you happen to be here, then you should grab some opportunities to witness at least one of this. However, the problem you may face in the east is that the lay back attitude during festivals keeps almost all markets closed in next 2 /3 days. If you are in Delhi, you can witness both.
I will be off to Dehradun to spend some time with old friends this extended weekend. The extended weekend means rush for hotel accomodation. If you do not have prior accomodatoion then you face face problem in popular holiday spots between 30th Sept -- 2nd Oct.