I think a key point that many have raised in the discussion is that iconic underwater images vary depending on where you live, what you are exposed to.
Iconic images are ones that have a cultural resonance and this depends on your culture, what you are exposed to, where you live. For example, in the US there is no surprise that iconic images tend to be ones from your National Geographic magazine. In the same way that in the UK, iconic TV usually comes from the BBC. And while Nat Geo magazine is sold all around the world, it has much less cultural resonance in the UK, as an example. I bet most members of BSoUP couldn't tell you what was the subject of the last UW feature in Nat Geo. I suspect most LAUPS members could.
However, as your talk is on the West Coast of the States, Steve, I suggest you bias towards what are likely to be the audiences' iconic images.
Alex
p.s. I am not so introspective about my photography (and like most photographers I am most excited by my latest work). To go back to Steve's graph, my aim (as is most photographers) is to to produce photos that end up as far up his line as possible. But exactly how much they end up resonating culturally is usually much more about where they get used (how widely they are seen) rather than any intrinsic artistic superiority. I guess I am saying you can't set out to produce an iconic image, you can simply aim to be as high up the graph as possible and then need factors beyond your control to give your photo the platform to make that last step.