Here's one i did before the actual casting process with Matt Damon as Cap. He was my top pick, but he's not the one, so whatever.
Here's one I recently did of Chris Evans as Captain America using a picture from Fantastic Four: Rise of the Silver Surfer. That costume lent itself well to the Bucky Barnes Captain America costume design, so that's what I went for. It's not exactly how I think it should be in the movie though.
I used that picture for several concept scenes.
Cap talking to Tony Stark
Cap talking to Nick Fury (I know the patch is on the wrong side)
Cap and Iron Man about to do battle
Cap and Iron Man about to do battle again
Here the link to my gallery if you're interested.
My Gallery
I plan on doing more of these using different pictures of Evans and maybe with different costume designs. Hopefully when some good pictures of Hemsworth as Thor come out, I'll be able to put the Big 3 together!