I don’t know if I qualify as a long-time user or not, but I can tell you I’m still finding actions I didn’t know about, or perhaps had known but forgot about. For instance, a few hours earlier I learned about the “Log” action, and a situation it might be useful for.
I don’t know of a unique list, but there’s over 150 non-unique actions, so it’s unlikely any of us remember all of them. But if you use the Edit->Insert Action->by Name menu item, you can generally find what you’re looking for much easier, because it can match on some things that are not in the actions’ names. Peter has some “alias”-type words that it will also match on.
As an aside, that’s the only way I insert action. You can get pretty quick at it, too. For example, I have F15 on my extended keyboard set up to insert by name. I can type F15 then s v x return, to insert a Set Variable to Text action. Don’t know if this is useful information or not, but I’ve already typed it, so I’ll keep it. 