Gore doesn't usually bother me but there's one scene in Halloween 3 - Season of the Witch...
*spoiler*
where the main guy (forget his name) attacks one of the robots in the factory and I think he punches him in the stomach and gets all this yellow goo on his hands and for some reason that bit just made me retch!
Sorry, bit of a pathetic answer I know, but I'm so used to seeing gore these days that I don't think I notice it any more, and this is the only time I can remember having any kind of reaction.
Of course sick films like Cannibal Holocaust are awful, dunno if it really counts as 'gore' though...
As far as actual content (as in gallons of blood . . .) the goriest are probably "Evil Dead" and "Day of the Dead". The sheer carnage in those two films was incredible.
and maybe it is not the goriest but who really knows the answer to that due to the fact that ..there are so many horror movies out ..you cant really compare now can you ?
Definately Peter Jackson's "Dead Alive", "Hellraiser", "The Evil Dead", and all 3 of Romero's "Living Dead" films have got to be the goriest ones I've seen.
One I have yet to see, though, is "Zombie" I've seen some clips and it definately ramps up the gore quotient!
(The eyeball impalement in particular stands out, I'm told)
Event Horizon has a couple of gory moments. But, no way in hell does it compare to just about every Takashi Miike horror, and it certainly doesn't compare to Brain-Dead