ThinkGeek is now selling an officially licensed plush Headcrab Hat. It sits on top of your head and doesn’t cover your face. Because that would just be silly.
The hat has an adjustable baseball cap-style closure at the back and is made of polyester. We think.
Prepare a crowbar and a torch and head to ThinkGeek to order the hat. It costs $30 (USD) and possibly your free will.