The only Harry Potter SI that immediate comes to mind is Magical Me, and it's what I'd call "almost recommended" at best. Though it did help me with a few of my own ideas regarding Lockhart.

I think the SI concept (or that of an original character with access to some plot knowledge) lends itself better to some fandoms than others. With Naruto, there's an entire world to play with, an infinite number of missions you can invent or tie into plot, and so on. The 'Rookie 9' and Team Gai are all characterized at least somewhat. With Harry Potter, every year takes place at a school (not the wider world) where there are tons of named (but not characterized) students available to be OCs who had a phophetic vision of another life.