Like others, I like the feature set of the Canon S90 a lot. My five year old Olympus is still going strong, but the new cameras give such a quantum leap in image quality I felt it was time to upgrade (I also got an Olympus E PL1 setup, for other uses). As with anything, there are pros and cons, but the S90 seems a good compromise for a small setup -- for underwater photography "lite".
I paired mine with the Canon DC-35. I realized that I could step up to a much more professional housing, but I kept my low cost constraint in mind. Again, there are pro's and con's, compared to the Ikelite and FIX housings. Another factor in my choice was being able to use the on camera flash; the Ikelite housing blocks it. I suspect that for macro, where the flash is most effective, the Canon housing will block the flash too, so I am considering making a light duct like on the old Olympus PT-023 housing.
I've thought long and hard about this. Do I get a just a housing and camera, or add some add on lens options to make it more versatile? When I do that, this setup becomes more costly and bulky, contrary to my "lite" goal. Ahh, tradeoffs. I decided to add a close up lens and wide angle lens. The cost of a good macro lens, wide lens, and adapter equaled the cost of camera and housing, so this was worth serious analysis.
I compared several add on lens "families": those that mount on 67mm threads, Inon AD, and Inon 28AD. To compare, I looked at three factors: add on lens
cost, lifetime, and breadth of suppliers. Cost seemed to favor 67mm, simply because there are a lot of used lenses available at good prices. Regarding lifetime, The 67mm lenses will probably have adapters for the next camera and housing I buy. Regarding multiple sources, there are many high quality 67mm macro and wide lenses. On paper, choosing lenses that mount on 67mm adapters looked more attractive, but I know it will be less convenient in use than a bayonet mount system. I may regret that choice, we'll see.
For a start I chose an Inon 165/67 close up lens and an Ikelite W20 wide angle lens. They were inexpensive and seem good quality, though I realize the W20 will vignette unless zoomed in, tough. The Fantasea Bigeye 67mm dome also looked attractive for this setup, I might try one. There have been reports of internal fogging occasionally with this Fantasea Bigeye, so I'm a little wary of it. It also seems more likely to scratch than the glass Ikelite W20. We'll see how this setup works out. I'll probably make a 67mm adapter myself, like this one:
Canon G9 & G7 housing - DIY 67mm lens adapter - Wetpixel :: Underwater Photography Forums
That's one person's idea on configuring a system for the S90. I'm looking forward to using this "lite" setup to make some great memories on my next dive trip (Cabilao and Apo Islands, Philippines in June!!! Yeah!!)
I know it's not a perfect setup, but a wise person once told me the best camera to use is the one in your hand --- technique is more important than equipment.