Nitroxinator, A620 is a whole different sort of camera to the A520, check out dpreview and do a side by side comparison and see for yourself.
Jamdiver, take the below for what its worth. I've read it, the tone seems critical but I really didn't intend it to be, I'm just too lazy to edit it at this point. I think you made a good point on the A620 that I wanted to respond to.
I looked at the A620 before going with an A520. For what I intended, the lower cost of the A520 outweighed the better quality of the A620. I have no doubt that the A620 would be superior to the A520. To me, though, the real issue is, as an underwater photographer, what do you intend and what are you willing to spend? I know a lot of divers that just aren't interested in anything more than see it - point -autofocus-shoot. Post process? Nah, too difficult. External stobe? Too bulky. Plan a shot? Takes away from the diving experience. And the list goes on - and they will always wonder what's the point in spending more than the minimum. There's already a thread on "Questions to ask an instructor before taking their photography course", and it will eventually become a sticky. Anyone want to split off an additional thread, "Questions you should be asking yourself when you decide to purchase a camera, and what you should be asking yourself before you take up underwater photography"? There are probably a lot of potential beginning photographers lurking this thread that would benefit.
Just as a point of reference, I started diving based on the idea that I was going to use it as an outlet to create artwork (mission accomplished). I had a camera and an underwater case before I'd even finished my openwater certification, even knowing that I couldn't use them on my openwater dives. I suspect this put me in a rather extreme minority of beginning divers.
I didn't mention it, but I would go with the S80 and the Ikelite housiong, even never having used the S80 underwater or topside, simply based on the specs. That does not mean that I know that its a good beginner camera. I acknowledge that I am by no stretch a beginner photography, I have a bias towards higher end equipment (case in point, I ordered the Sony HC1 over the weekend, can't wait to get THAT underwater). I rate as one of those photographers and soon to be videographer that, realistically, started over the deep end and it was probably never a hoobby, it has always been an obsession. I thought about opiniating, and then reconsidered and stuck with specifying information about the one camera in the list that I had specifically used.