Well, if you're just starting out, it would'nt be a good idea to load yourself with too much tasks underwater.
Hence, it would be better to start with something that is easily handled - something small - probably no external strobes for the moment.
I've used Olympus, seen Sony, heard about Canon.
These 3 are by far the most popular because the underwater casings are cheap comparatively - in the range of $300 +- $50.
I used a C3030 and switched to a C40 - because of size. Both have produced really nice photos.
Some of my friends use Sony and their photos are not too bad either.
The Canon A80 would be one of the best options. IMHO.
Olympus - If you were to go for the 50x0 series, it's gonna be rather huge. One handed operation is not really that easy.
Olympus housings also utilise a diffuser to soften the harsh flash. They also have a counter weight included to make the housing (with camera) more neutrally bouyant. (I'm not too sure about other housings)
I'm using the C40 which is really petite and I love it. But I don't think they sell it anymore. Some features are missing in the C50. C40 uses the Smartmedia which is becoming obselete. So, this won't be a suggested pick.
Sony uses the memory stick which is one of the most expensive memory format.
Canon uses the Compact Flash which is great - cheap, huge capacities available, common, etc. The A80 is really impressive. Rotating LCD, AA, CF1, Budget Priced, Housing up to 40m, 4Mega. You should look this one up. If my c40 were to die on me, this might be my next choice.
If you wish to upgrade to external strobes, you can simply purchase the Sea & Sea strobes and arms. Some are designed to suit digital camera use. But they do cost a lot - about $1K. These can be used with any of the camera and their casings mentioned above.
The casing from the original manufacturers usually lets you go down to about 30 to 40m max. If you need something deeper, the Olympus range (C50x0), being more popular with underwater divers - has a whole range of 3rd party housings from Light & Motion and Ikelite. These let you go really deep.
Some advise I had from Experts:
- Shoot upwards (photos will not be so flat)
- If you think you're near enough, get even closer.
- Improve your buoyancy control - Save the Reef.
- Stop eating shark fin and turtle soup
I've yet to see a shark and turtles are sometimes hard to spot
Read this site for Good Underwater Photography Tips
It's hard to get a good dive buddy. It's even harder to find a good dive buddy who also takes underwater photography. (Yet to find one)
So chances of finding some here are relatively high. As pointed out, try the thread to see if you can find a kaki.
If you're looking for a good dive shop, I can recommend my friend @ Trekkers.
Trekkers Website
They are a great bunch of guys and gals. Very outdoor kind. If you like, you can give them a try or just drop by the shop for a peek.