Slickdeals has a coupon code section.
Get the best deals on your favorite online stores to help you save money on anything and everything available online, in-store and near you.
coupons.slickdeals.net
There are also browser apps that search for them, but they probably collect browsing and purchase data.
Rakuten is a thing too. I've gotten a couple checks in the mail from them, IIRC, after accummulating enough points. I like what Honey does for my Amazon shopping. It checks other retailers too and tells me when they have a better price than Amazon, but mostly I use Honey to watch for price drops on Amazon. When I'm alerted to one, I hit the link (comes to me via email) and then check out the price history. That defaults to 30 days (at least for me), and I change it to 120 days (the max) and I have a good idea if I'm apt to get significantly better price if I wait. It's save me a fair amount of money. Also acts as a reminder that I'm interested. Seems like more than 1/2 the time I get a price drop alert via Honey by the time I check out the link (usually within hours), the price has gone up and I'm not interested. But I've gotten a lot of good deals via Honey alerts on Amazon accessible items. I'm not on Prime, so I go by the now $35 free shipping threshhold. I keep stuff in my Amazon cart or in their Save For Later section, which for me is hell of full of stuff (a lot of which I am not thinking about buying, but keep there because I might want to check out reviews, do more research or whatever) !
The only time I get coupons pretty much is when I go to a new website (for me) and a popup offers a coupon. Those are from the retailer, I figure, just automatically pop up when you're new. I figure they use cookies to keep tabs on you, but I'm not very internet savvy in that regard.
I've used Slickdeals too, pretty good site, but haven't checked them out for a while.
I do a fair amount of Ebay shopping, much of it used. A whole lot of the time Ebay is not a good place to get something, Amazon for one often beats all deals on Ebay, including Ebay used stuff. But if you know what you're doing Ebay is a good (and cheapest) source, plus they back you up if you don't get what you have a right to expect.