Iron Man

When Pepper Potts walks in on Tony Stark being undressed by JARVIS’ robot arms, at around the 1h30 mark, in the background you can see a half complete shield that matches Captain America’s red, white and blue design. According to the exclusive Walmart comic book that came with the Iron Man DVD, Howard Stark (now rumored to appear in Iron Man 2) created the shield’s technology and Tony is using an old discarded prototype to create an alloy for his suit’s armor. This implies that, rather than creating the shield, Tony Stark is taking it apart, as previously rumored when the shield was first spotted.

The Incredible Hulk

On the 3-disc special edition DVD there is a cut scene set in the snowy north where Bruce Banner goes to commit suicide, before turning into The Hulk and starting an avalanche. As the snow crumbles you can just about make out the outline of a human body and shield, meant to be Steve Rogers frozen in suspended animation, first spotted by Film School Rejects.

Other hat tips to Captain America include mention of the WWII ’supersoldier serum’ created by Dr. Reinstein, as injected into Emil Blonsky. Incredible Hulk director Louis Leterrier comments on this (IGN):

I wanted to address because I thought it was fun. But like Dr. Reinstein and Vita Rays, that actually was done on the day because we wanted the super serum. And the prop master said, “What do you want me to do with this?” And I said, “OK. Give me the serum.” And he said, “What color should the serum be?” I said, “Blue like Captain America and I want the cap for the vile to be red like Captain America.” And he said, “What do you want me to put on the sticker?” And I gave him Dr. Reinstein and Vita Rays;

The appearance is at 2:25 in this video, not that you can really see it in this quality: