IIRC, he tried to do something like this at DragonCon a couple years ago, but the fire marshalls made him stop.  The marshalls were pretty proactive about crowd formation there.  Just go to his regular signing - 4 hours early. 

I'd gladly take the credit, but I wasn't at that DragonCon.   I believe that may have been Pamela?

The very first kick in the gut moment I thought of when I started reading this thread still hasn't been mentioned: The last page of Changes.

Unlike a lot of the others mentioned, it loses a lot of its impact on rereading, because you know it's coming, and even more-so, you know it can't be permanent (one way or another). But thinking back to the very first time I read it, the day after it came out in hardcover, no spoilers on line, no hints from friends who'd read it before me. Completely out of left field. I was on a break at work at the time, and I literally sat there staring at the page with my mouth hanging open for more than a minute. And then I cussed a blue streak at the evil bastard who'd end a book like that for five. And then, of course, I went home and read the whole book all over again. 

• Red Court vamps ripping off Harry's clothes and tormenting him at Bianca's in GP because he is so, so, so helpless;
• The Denarians subduing Ivy at the Shedd in SmF and the despair Harry and Kincaid suffer from it;
• Harry unleashing the bloodline curse at Chichen Itza (especially as read by James Marsters);
• And, of course, Tessa blowing a kiss at Harry before opening fire on Michael in SmF.