Neogaf user Mama Robotnik has a habit of unearthing incredible Retro Studios Metroid art, and as a massive fan of Metroid Prime, I'm always appreciative. Personally I love this kind of thing, especially when it's from a game/series that I truly adore. Some of this art is quite gorgeous, some of it gives a cool insight into development.
I really like this hand drawn stuff, like this Mecha Ridley...
And this Omega Metroid...
I have no idea what this is.
There's also some cool renders and such like.
Head to the Neogaf thread for more stuff.
Thanks Mama Robotnik!