I'd go with Ikelite housings and ports, probably.
For lenses:
Sigma 17-70 with dome port A friend has been using this lens for a while now and I borrowed it the other day. I like it so much I'm buying one today (I have to give his back because we are on the same trip next month and we both think it will be a useful lens!). It focusses closely so you can minimize the water between you and your subject. The range is really nice for a tremendous range of subjects and compositions. It's pretty fast to focus and it's sharp. It can also be lit pretty effectively with a single strobe. If you want to see a few examples, have a look at the last two photo links in my sig from my first time out with the lens. For $350 ish at sigma4less it's a no brainer in my book.
Canon 100mm macro This is a sweet piece of glass. Fast to focus, though you will likely need a focus light for dark shootin. It allows you to fill your frame from a bit away from your subject so helps with skittish creatures and with keeping your distance from behaviours so as not to disturb. Add TCs later for getting fabulous supermacro stuff. It's relatively easy to light. I personally have found that I don't need the extra distance for most of my shooting so my favourite current lens is...
Canon 60mm macro This is the lens that I almost always reach for. It allows 1:1 just like the 100mm macro above, but you have to get closer. Closer is better underwater. However, as with everything there are tradeoffs - closer is harder to light properly sometimes and sometimes creatures won't let you in that close. So far, for my area, I haven't had a problem getting close enough to fill the frame on even the most skittish creatures like mantis shrimp and gobies...ymmv. I adore this lens. It is also a bit more versatile than the 100 as with the wider field of view you can actually shoot reasonable sized fish and turtles as well as diver heads etc. I have a well framed shot from behind a diver's head as they aim their camera at the turtle in front of them. Diver, camera and turtle all in frame. I wouldn't be without this one.
Canon 10-22 or Sigma 10-20 These are the ones for wide angle work. You will really need two strobes to do justice to them, though. I had the Sigma but flooded it
It was a nice lens. I changed to the Canon simply because the budget did allow after the flood. It's a fabulous lens - I love it above water. Haven't had it under myself as yet, but the images from it from others are wonderful.
Woody's dioptre or similar Add this to your macros for more versatilitiy underwater. Check to make sure it fits the Ike ports. Great equipment for like $70!
Strobes
Ike 125 The big boy of strobes. Quickest recycle time. Great coverage. Proprietary batteries.
Inon 240 I use the Inon's and just ordered a second. Light, easy, great coverage, manual control, AA batteries (my rechargeables last forever it seems).
Hope this helps