You can also go to company or product websites and see if they have coupons available. Sometimes you can sign up for a monthly newsletter that will come to your email address with special offers or coupons. 3 or 4 times a weeks I get a email from someone with coupons attached, so its a great resource. Many companies that produce organic products have special mailouts/booklets with lots of coupons in them.
At Walmart, look for the "All You" magazine. It is a treasure trove of coupons every month.
I have also used a site called "Coupon Clippers". You pick the coupons you want (some may have a minimum order) and pay a small handling fee per coupon. Then she mails the coupons to your home. I've always gotten mine within a couple of days. This is an excellent way to get multiples of coupons you really want and need. I've stocked up on my Lipton Tea Bags and my Knorr Rice and Pasta packages this way. She lists full details for each coupon, so when you order, you know exactly what you are getting.