www.DontPayFull.com is a pretty reliable one. There is alsoLog In. These require printing, so you'll need access to a printer. You can also useLog In, which is an e-coupon site. What you do is link your store loyalty cards to your account, choose the coupons you want, and go shopping. The savings won't happen at the register, but you'll see the saved money in your account and you can transfer it over to your PayPal account. As for coupons in the mail, I usually just open up a weekend newspaper. Sometimes, the lobby of my apartment building or my work will have some newspapers chock full of coupons. But, I've never purchased the Sunday paper for the coupons - but I hear that the coupons in there are great. Another thing to do is just shop the sales and see what the actual grocery stores have discounted. Stores like Safeway and Harris Teeter will let you log into your loyalty card account and you can put e-coupons right on the card. So, the savings will take place when you swipe your loyalty card at the register; no need to worry about paper.
The previous poster has lots of good information. I will caution you on the sites that you print coupons from as they can put a lot of adware/malware on your computer. There are lots of good blogs out there that will do coupon/store match ups for you. Googling one for your area is best so you can make sure you are comparing your local ad to what coupons are in your paper. Coupon inserts in the Sunday paper can vary by region.
It depends where you're located. I personally use websaver.ca and save.ca. So far, in the last few months, I have saved a total of $30 on stuff that I normally purchase, such as soy beverage, bread and cereal. These are only Canadian, though, so I'm not sure of any American websites.
I never seem to be able to get the coupons to print at home. I'm sure it's something with my computer. I wish more retailers would offer mobile coupons. I like Saving Star. No coupons to mess with. It's had some good deals.
You have to be careful about coupons and savings cards. Some of them are scams. Note, as you might expect, many can be found on social media and often they are used to gain hold of consumer info to be used for identity theft. Anyway, myself, I've bought some food cards off of eBay and now I am convinced they are some sort of a scam. Nonetheless, I was able to use many of them at this one fast food place. However, I feel kind of bad now, cause I think the cards might have really been phony.