Similar Sites for Other Video Game Systems?

You need to first make an account at gullible.net

That subreddit is the best one. There are several other relatively large subs that do similar things, but are either not maintained that well or have too much clutter (bunch of shovelware for example, on FGF they have a separate thread for those).

You could also use websites like GG.Deals, Dealabs (French, it has regional sister websites), etc.
You won't find much however... You will usually only find the "real" deals (free or huge discount) on PC, not console. One of the 65174 arguments why it's called the master race.

Unrelated but since you're on PS, the latest post on that sub is about free PSN avatars for some PS+ event.