Seen them all and I have to agree with Leykis, there are many films out there that are FAR more violent. He named many and the Jap stuff is really twisted. As far as the list:
I prefer the original "I Spit On Your Grave"
Hostel is great, saw the 2nd on my honeymoon. The first one gave me the feeling, "This could happen to a bunch of stupid fucks like these guys"
"A Clockwork Orange" is a classic and my favorite movie of all time, hands down. But really not that violent when taken in context.
Wild Bunch is a great western. They ran out of fake blood in the first 3 days of shooting.
And really, 300? I would have chosen actual classics like "Scarface" or "Last House On The Left"