Rarest Lego Star Wars item - Vaders Mask, the best collectable

I was reading over at Yahoo Answers and someone asked what the rarest Lego piece would be. Well this is a Star Wars Lego Collectables blog so for this I was thinking maybe the Boba Fett minifigure from the Cloud City set. This photo shows the difference between the regular Boba Fett minifigure and the super rare one.But, to be honest, the absolute rarest Star Wars Lego piece would be this - the protype piece for the Darth Vader Helmet! For some reason Lego makes the prototypes in red plastic, maybe it makes them stand out, I don't really know why.
Sorry about the photo, it is the best I have. And, of course, it was never for sale and impossible to get!
So there you have it - my choice of the rarest Star Wars Lego Collectable piece!

Lego Building Instruction for 7676 Republic Gunship

I have posted photos and details on the yet to be released Star Wars Lego 7676 Republic Gunship before, the one with 5 Star Wars Lego minifigures - 2 Clone Troopers, Asajj Ventress (will be a rare collectable), Obi-Wan Kenobi and Plo Koon (will be a rare collectable).
Well it is still not released but you can actually download the build instructions from Lego themselves!!! Download them and try to build one with spare Lego you have laying around.
Here are the links :
Star Wars 7676 Republic Attack Gunship Building Instruction Part1 - Download size: 11.14 Mb
Star Wars 7676 Republic Attack Gunship Building Instruction Part2 - Download size: 11.33 Mb