Shelton beating Triple H in his Raw debut was pretty damn awesome. Along with his WM21 MITB ladder run were two markout moments.
Benoit winning the Title, making Triple H tap and him hugging Eddie was insane! It was really emotional at the time...
Jeff Jarrett winning the IC title with the Sharpshooter and crying out for Owen, also amazing.
TAKA Michonoku getting a world title shot against Triple H and almost winning. (I SO thought he was gonna win.)
The Rock...well, everything he did was a mark out moment for me.
Stone Cold getting run down in the first place was up there.
Matt Hardy jumping out of the crowd and attacking Edge, then cutting a promo telling the WWE to "kiss my ass!" had me going "It's real! It's real!". That was epic.
My favorites that happened that were mentioned already was when Sting dropped the bat and the "American Badass" debuted. Great thread, Mike.