the best addon is Keepa, they have a time series price tracking thats added right in the page

I’d also recommend JungleDealsBlog

Slickdeals.net also good. Owned, iirc, by some bank though. Comments seem genuine and let you know if it’s a real deal or shill post.

I use Slickdeals all the time. It's pretty great, but has had a lot more advertising both blatant and stealth in recent years. Still good site though, I'd also like to know any more deals sites though.

And I also wonder how is there not a legitimate coupons site? Or is there? Even slickdeals now the coupon codes section is trach similar to retailmenot and the multitude of other crappy coupon spam sites.

Slickdeals used to be a good source for legit coupon codes and sometimes they are still on there but you have to dig in the forums the actual "coupons" section of the site is spam.

On a slightly more than cursory inspection. That site sucks.