There are many ways to acquire coupons. They can be found in newspaper circulars, magazines, printables online, peelies, blinkies, on products themselves and you can ever get them sent to you by mail.
Also dont forget about sites such as Upromise which will load coupons directly to your store bonus cards. Upromise also gives you a percentage back on all purchases made with your registered bonus cards.
Additional coupon resources:
Kmart Coupons
CVS Coupons
Rite Aid Coupons
All You Coupons
Campbell's Coupons