I think Ikelite did say sometimes in the past that Fuji S3 will fit in its Fuji housing. Unfortunately I think that for the price, the improvement in the CCD does not quite offset the higher price than its competitor and the improvement in the ergonomics over S2 was not very significant. Since its release, there has not been a lot of talk about it for underwater use anywhere I can see. I second the D70s or 20D as a good place to start. The 350 or D50 may be a bit cheaper but when you are done with everything else, the price difference is very minimal so you might as well get a camera that has a bit more feature/ergonomics for long term use.
Olympus dSLR is interesting with cheap housing available but lens choice is still limiting and some lenses are incredibly expensive so in the end, you won't save that much more money.
On tricky thing with depth of field, digital PnS actually has incredible DoF. Oly C5050 at F8 has a hugh depth of field in comparison to dSLR at f8. Of course you are stuck with F8 with c5050 but depending on lenses that you use with your dSLR, you can go up to f30's-50's even. I tend to shoot most of my macro shot around F18-22 but depth of field is not wider than C5050.
btw I believe that at the same f-stop, dSLR DoF is a bit wider than film SLR also.
Olympus dSLR is interesting with cheap housing available but lens choice is still limiting and some lenses are incredibly expensive so in the end, you won't save that much more money.
On tricky thing with depth of field, digital PnS actually has incredible DoF. Oly C5050 at F8 has a hugh depth of field in comparison to dSLR at f8. Of course you are stuck with F8 with c5050 but depending on lenses that you use with your dSLR, you can go up to f30's-50's even. I tend to shoot most of my macro shot around F18-22 but depth of field is not wider than C5050.
btw I believe that at the same f-stop, dSLR DoF is a bit wider than film SLR also.