So what piano solo score should I add to my collection next? some Monster Hunter? or maybe more Final Fantasy?
It's your turn to decide.

Currently in my collection.

Super Mario Series Super Best (Intermediate) Alfreds Music Publishing.
The Legend of Zelda Series Super Best (Intermediate) Alfred Music Publishing.
Final Fantasy IV Piano Solo Sheet DS ver.
Final Fantasy Super Best Piano Solo Score 2010

So any suggestion would be appreciated. Any videogame music goes from beginner to intermediate difficulty level. Does not even have to be videogame music. most important this is that its beginner or intermediate difficulty level.

I have bought my books from squaresound.com and otaku.com.

From VII onwards the FF piano collections start to get pretty difficult, but some of the the earlier ones (IV and V for example) have some easier arrangements. I bought mine off play-asia.com

I've only heard one piece from FF. It's the Advent Children-Those Who Fight, which I'm guessing is one of the harder pieces. I was quite shocked how much I enjoyed this piece the first time I heard it. I have never played a video game.

Here's an excellent performance by I'd guess a classically trained pianist:
http://www.youtube.com/watch?v=7dqH7TQePyI

I hope that I can propose my own work, without being dragged down as spam (???) I'm still uncomfortable with this, but I guess I'll contact Frank next.

There's a work I did, which is for intermediate students: http://www.musica-ferrum.com/catalog/viewitem.php?show=4 It's got 21 short works in there, in a bizzare setting, and it's illustrated in B&W by a great artist. There's a few youtube videos if you check in youtube (and there's one in the page that I linked).

And I recently found out about a work called 'The Big Witch Pianobook' which is close to my own 'Sketch Music' in a way. I've still to find a way to order it, but once I do I'll let you know cause it seems brilliant!