Steampunk Iron Man, the Marvel Costume Contest Winner at New York Comic Con 2010 - looking at a small pic of this, I didn't immediately realize it wasn't a still from the film. Had to show my husband - the comic geek in this house.
Jen of Epbot attended this year's DragonCon in Atlanta. She snapped photos of amazing works of cosplay, such as this incredible Cyberman from Doctor Who. You can see more of her cosplay photos at the link.