Billy Magnussen appears naked in the episode 6 of season 3 of Boardwalk Empire. We get great views at his butt and partial views of his penis. Billy Magnussen seems to be circumcised although we can't be completely sure from the shots.
Vincent Piazza is naked and making love to a woman in season 1 episode 6. We see him naked from a distance at first and then when he walks towards the camera we see his nice uncut penis.