Welcome to the addiction!!! You will find that there are many options and even more opinions on what cameras to start out with. The Pink Link in my signature below includes some getting started information including a list of some specific options and links to images/discussions about those options.
Knowing things like: your budget, how often & where you dive, what kinds of images you like (or think you will like to take), if you have a digital camera already, if size is an issue, how experienced a diver you are and how comfortable you are with a camera will also help us point you in the right direction(s)!
I personally adore the Canon A series offerings. There are many different models out there in this range to suit most budgets and most of the needs of divers just starting out with underwater photography. These little units have lots of growth potential so you won't be looking to upgrade the week after you buy it (well, if you're like the rest of us, you will coz this is a slippery slope for shopping!)
Fuji and Olympus also have some good choices including the Olympus 350 which has RAW (see the Pink Link for more info on that).