You've already seen the Portal Halloween costume - now here's the Team Fortress 2 one (click pic to embiggen).
Extramegoultra bonus points for actually fricking building the Heavy's gun.
Big thanks to Thiefsie for sending it over. Its original source has been located here, where you'll find a bunch of other images of Janvitos and his RED chums.
I wouldn't like to say which one is most awesome. Because they are both awesome.