I'm just going to drop this here:
Top Dean Winchester Gruesome Injuries, as chosen by TheWinchesterFamilyBusiness.Com. Ah, the greatest hits of H/C fandom.
Though I gotta say, some of my favorite H/C footage is pretty understated/actually not that gruesome, all things considered. (If for some reason you have a spare 17 seconds, there is truly excellent footage of Dean sitting in a chair in S5. I think it's probably 5x20, after Crowley feeds him to Brady/Brady's proto-SucroCorps digs. It's an underappreciated chair-sitting moment, okay! XD I'm also pretty fond of Dean coughing up a wood chip in 4x06. Which isn't gruesome until you think about coughing up a wood chip.)
Things I'm surprised didn't make the list... Hm. Getting turned into a vampire in 6x05, though I guess I'm not sure if that was gruesome so much as "well, this is as pleasant as the first scene of an episode of Special Victims Unit, just before the theme song rolls."
Maleus Maleficarum, though. Which is...3x09? In any case, lying on the ground, coughing up lots of blood.
Wonderful, stupendous! Classic hurt!Dean scene, right there. XD I wasn't in fandom yet and didn't even know what H/C was, but I remember specifically choosing to watch that episode because the insinuation of this moment was mentioned in the synopsis.
Thoughts/feelings/orgiastic responses to the moments mentioned? Scenes you want to add to the list? Scenes that don't actually exist but you'd like to share from your Dean H/C wishlist? Lay 'em on me. ;)
EDIT, 18 Sept 2013: WinchesterFamilyBusiness is currently down. :( Hopefully the site is back up and running soon!