Here's a great bit of work by LoganX0. Not only has he drawn an imposing Captain America (I like it when the chainmail/scalemail actually looks like metal armor) but he's also tapped into the early years of the character by using the beaches of Normandy and the D-Day landings as the setting for the image.
Sticking to the grey palette here was a good call I think. It adds a somber note to the whole image. The choice to angle the composition is an interesting one too. It gives the whole thing an off-kilter feel.