I made Gordon here out of several G.I. Joe Sigma Six figures. The head came from an Arctic Duke, while the torso, upper arms and thighs came from a Frontal Assault Duke. The forearms, hands and lower legs came from a Hi-Tech figure. The glasses were hand-made using the plastic from the figures' packaging and the crowbar is a 1:6 scale Power Team SWAT accessory.
Now, the hardcore fans out there will be the first to point out that this suit is not game-accurate for either of the iterations. I will freely admit that, but I justify it as I will the rest of the figures in this custom line, by saying it is my "Saturday-morning cartoon" interpretation of the characters, a sort of Half-Life: The Animated Series, if you will. Thus, I dub this suit the H.E.V. Mark X, where X equals any number that Valve has not officially used. Anyway, now that that's out of the way, you may choose to...
Read about the entire process from start to finish, here
Or, skip ahead to the final product, here
UPDATE 2/25/2010 - After a couple of years sitting in a display case, the Craft Porcelain pieces of this custom continued to dry out and shrink until they no longer fit properly. I was forced to come up with a more permanent solution and so I took the opportunity to also redesign a few elements. To see the custom as it appears today, click here