We have an Inon strobe (D2000, I think), attached to our Canon housing. You can get a number of cable options for different housings, we use a simple fibre optic cable that works very well. We bought the strobe for the previous camera, an Olympus, (which I subsequently flooded) and were able to make it work fine with the Canon. The housing has a separate difuser which clips on to the lens portion for use without an external strobe, the fibre optic cable attaches to that with a couple of little screws. The only minor issue with our set up is that you have to stick a small "filter" tape over the actual camera flash inside the housing first (tape came with the strobe and is reusable). This lets enough light through to trigger the strobe but doesn't cause any backscatter issues. Just remember to take the tape off when you're taking post-dive photos in the bar in the evening.
I'm sure with other camera/strobe connection cables, this isn't necessary.
The Inon has numerous arm arrangements and can be made a double as and when your wallet and photography requirements deem in necessary.