There's some pretty good guidance here, but let me toss out a few more ideas.

I do use some e-coupon sites that don't come off at the register, which means you can use a paper coupon AND get the e-coupon credit. The e-coupon money adds up over time, and when you hit the minimum disbursement ($5-10, depending on the site) you can request payment. Some pay by paper check, some by direct deposit, some by paypal, etc.
Upromise.com I've been a Upromise member since Oct 2001, and they rock. In addition to grocery e-coupons, they offer cash back on your online shopping if you shop through their website. You link your grocery & drug store cards to your Upromise, load e-coupons and shop as usual. There's an email every time there's new coupons, you just need to go load them. They market themself as a way to save for college, but there is no requirement to do so, you don't even need to have kids, and they'll just send you a check. They process checks quarterly, if you ask for one, and, last I checked, the minimum amount you need to request a withdrawal is $10 (used to be $5, check the current rules before withdrawing). Using the online shopping, with more stores offering shop online pick up in store, I've earned a couple bucks this year already just keeping my husband ordering online when he realizes he needs to run to Lowes for screws or a new bit or sandpaper or whatever. And it saves money because he's not browsing, his needs are waiting at the front of the store for pick up.

Savingstar.com I've been doing Savingstar for almost 2 years now. I got right on board when I saw them start their own e-coupons because Savingstar actually manages Upromise's e-coupon program, so I had faith. The e-coupons don't come off at the register, but they add up in your Savingstar account, and once you've hit $5 you can request pay-out. They do paypal, and I think Amazon GCs. Just link your grocery & drug store cards on Savingstar, load e-coupons, and shop as usual. I've been preferring Savingstar to Upromise for my grocery e-coupons because Savingstar has a smartphone app, and I can check for new e-coupons and check the e-coupon list from my smartphone (no printing a list or relying on my memory in the store).
There's also Ibotta, but you have to use a device to do Ibotta (smartphone, iPad, etc). Savingstar and Upromise can both be done from just your computer. I've not yet done Ibotta. Mostly Ibotta requires you to photograph the product barcode and receipt after loading the offer. They've recently added a few stores that you can load your store card info like Upromise and Savingstar. Ibotta frequently wants you to watch videos, post to FB, etc to increase your e-coupon value.
I really like Savingstar and Upromise. It's a level of security against my husband's shopping habits. "I was out of deodorant, and it was BOGO at CVS so I bought 2." *sigh* I have a year's stock, and I have coupons, but at least he used the CVS card, and it was BOGO, and I had a 50 cent e-coupon on Savingstar. Could have been worse.