There are number of coupon sites out there and many will waste your time because the coupons and promotional codes are not updated daily.  Which site you decide to use depends alot on the types of stores you like to buy from.  I have made a short list of the coupon sites I use

couponstan.com

makemyshop.in

hotindiadeals.in

freekamaal.com

One of the other biggest advantages of online shopping is the competitive pricing. I think Amazon, Flipkart, Myntra offers great discount . Recently the End of Season Sale on Myntra attracted millions of potential customers.
There are few sites which more coupons and deals for this e-commerce sites.
coupondunia.com
hotindiadeals.in
freekamaal.com