Designer Brian Cargile (aka TwoHornsUnited) created the wonderfully detailed Aperture Science Portal Gas Mask. Cargile has already made an impressive array of science fiction-themed gas masks, many of which utilize neon lights and intricate designs.
The Portal Gas Mask was inspired by the video game 'Portal,' in which you play a character who wields a portal shooting gun. The design for the portal gun was absorbed into the contours of a gas mask, creating something that is recognizable on two levels -- a portal gun (for fans of the game) and a gas mask.
The mask is purely for aesthetic appeal however so don't mistake it for a functioning breathing apparatus during an airborne toxic emergency.