Spot the Namor reference in the above concept art from Captain America: The First Avenger?
To the left sees the "Underwater Cities Of The Future" from Atlantis Enterprises, of course with Atlantis being the home of Namor.
In addition, the scene at the World Fair depicts "The Synthetic Man," which is a homage to the original Human Torch, a member of the Invaders of which Namor and Captain America were also a part of.
Captain America: The First Avenger director Joe Johnson did state at one time that the Invaders were supposed to appear in the film, but then backtracked his statements by explaining it was a name they were considering to be used for Cap's team.
As we see in the footage below, the Namor Easter Egg never made its way into the film probably due to the character rights being possibly owned (or in part owned) by Universal.
Artist Adam Brockbank is responsible for the concept art.