Hands Down, Who's Got the Best Chin in MMA???

In your honest opinion, who has the absolute best chin in MMA? Were talking about someone who can take solid shots, possibly right on the button and keep on fighting.

Personally, off the top of my head, I have to say Chris Leben. I've seen Chris take a shot, watch his eyes roll and then watch him push forward to knock out his opponent with strikes of his own not long after. I don't recall the exact fight, but I'll dig it up and post a link to the video if I can find it.

~ Shane