It seems the consensus is to post the links to the al-Qaeda video showing the murder of Nick Berg. The reason can be found here:

I’m describing this in detail because I don’t want anyone to watch this without being really prepared.

When the Daniel Pearl video was making the rounds on the web, I refused to post a link because it was so soul-wrenching that I thought people didn’t need to see it. I thought September 11 was a big enough shock to the American public that we wouldn’t dare go back to sleep.

Unfortunately, I no longer believe that, and that’s why I’m posting a link to this goddamned obscenity. Watch it, if you think you can. It’s going to make you sick, and it’s going to make you mad.

And remember this: what you see in this video is what the mujahideen would like to do to each and every one of us.