This hit is as brutal as they come. Anquan Boldin went up for the ball, when Eric Smith met him in one of the hardest helmet-to-helmet hits you'll ever see.
As with the DeSean Jackson-Dunta Robinson hit, both the hitter and the guy on the receiving end went down for a while. This is the other hit on this list that I saw live, and it was really scary. On the video, someone commented that they were at the game, in the upper deck, and were still able to hear the hit, which is pretty amazing.
Boldin broke multiple bones in his face but still ended up playing a couple of weeks later. It's a testament to his toughness that he was able to come back and still go across the middle after such a rough hit.