Hey Fouremco,
This is an incredibly open ended question that you've posed, but since you mentioned the S80 that narrows things down considerably.
Digital cameras are always going out of production... even the latest and greatest model is but a year away from obsolescence with the current rate of change in the compact end of the market.
I would still go with the S80, just because it's no longer being made doesn't mean that you can't find it in stores.
And I also suspect that the Canon housing can be easily found on online retailers for months/years to come.
Ikelite also manufactures a housing for it.
There are also the A series cameras from Canon, the A520,A540, A620 and so on..
Of those i'd recommend the A620, manual control, wonderful image quality, quick operation et cetera..
But that is also out of production

..
One big drawback of the A620 is that in the canon housing it's not possible to add external third party lenses such as macro or wide angle.
You'd have to get the Ikelite housing to do that..
So in order of preference noting that you mentioned Canon in the title.
I'd go with.
- Canon S80
- Canon A620
- Canon A540
Have a look at
Dpreview's canon section, that should give you an idea of all the current cameras.