Hi Jrock,
Not sure if you've already purchased the Canon Housing for your G9, but if not, I would make sure that's the housing that will meet your current and future needs.
I've been doing my homework for quite some time and finally decided on the G9 w/ the Patima housing (
http://reefphoto.com/index.php?main_page=product_info&products_id=2873). I'm not saying you should buy the Patima housing, because it's very expensive, but I like the fact that it will allow me to take it with me on my deep technical wreck dives.
However, if you would like to add wet lenses to your camera, which I suggest you do, because it makes all the difference in the world, I'm not sure you can do that with the Canon Housing. I currently use an Inon Mount Base and several Inon wet lenses with my Sony Camera and Sony Housing, but Inon does not make anything compatible with the Canon G9 Housing, because of the oval shape of it's port. Consequently, you may want to consider the Ikelite Housing (
http://www.ikelite.com/web_pages/5can_g7.html), because they have options with that housing that will allow you to add wet lenses.
With regard to your question about which strobe to add to your system, I personally love Inon strobes. I currently use dual Inon-240 Strobes, so my first instinct is to recommend Inon strobes. However, I'm not sure how you would connect them to the Canon Housing, for the reasons I previously indicated.
If you do ultimately go with the Ikelite Housing, then I would probably tell you to consider Ikelite strobes, because there are certain compatibility advantages.
My suggestion would be to give the folks down at Reef Photo (
Reef Photo & Video!, The Underwater Photo Pros) a call. They are a speciality underwater photography store here in Ft. Lauderdale, and they also are one of the best known online specialists. If you give them a call, they would most certainly be able to give you some recommendations.
BTW, take a look at my Scubaboard Gallery if you want to see what you can do with wet lenses, as all the pictures within my gallery were taken with a simple Sony point & shoot camera with Inon wet lenses - I wouldn't dive without them! Furthermore, I also plan to use Inon wet lenses with my Patima Housing.