Man the shark one really gets me. Everyone thinks it's so damned real. My GF's stepdad had it set as his wallpaper with a description claiming it was the "Picture of the Year" for some website. They had a long drawn out explanation of where the copter was, what kind of shark it was, who the military guys were, etc. that was completely wrong. The first thing I do when I see a crazy picture on the Internet is head over to Snopes. Everyone else should too!
I'd say one of the most famous pictures is:
<IMG SRC=http://www.edge-inc.net/images/humor/full_car_load.jpg>
Classic!
-Lasereth