Coupondunia is the largest coupon websites and it contains coupon for every sort of products ranging from mobile recharge to utility bills. They offers exclusive coupon of some websites with whom they have tie up.
Most interesting this is that it also shows that when it was last verified and no of person who have successfully used it. Outdated coupons are removed from the websites daily and their coupons are genuine and credible.
User interface is very good and category wise coupon list are available. They also send daily alerts of best deals and coupons to their members on their mails.
There are regular updates of offers on their app as well. Other websites one may consider as couponrani, freekamaal, coupon.hindustantimes as they too have good no of coupons.