This is 2nd hand information, since I don't snorkle, nor do I have an underwater camera. However, what I keep reading when this question is asked is that if you're going to spend the money for an underwater camera, you're probably best served buying a good SLR of some sort (digital or film) and and underwater housing for that. then you have a versatile camera for both above and below the water.
There are often inexpensive housings available for the point-n-shoots- I could have gotten one for $130 for my Olympus 2MP camera. Now that I only have the D70, it is $1k or more.
I've thought of getting a Coolpix or something and a housing and using it only for snorkeling (and emergency backup camera) on trips. My wife could also use it other times, when I have the big camera, without worrying about $2k of equipment.
me and my dive buddy have had good luck with the canon underwater cases. $130-200. Add whatever canon digital camera, some have underwater modes ie the powershot A85 and you can get underwater and clicking for about $300-400. down-side is the flash. No external flash attatchments. Works well when less than 6 feet away in the carribean at 40 or less feet. As you go deeper, the closer you need to be to get the natural colors to show up and penetrate thru the water from the flash on the camera. Nikon also has nice set ups but they are very expensive.
Unfortunately, I haven't been able to find an underwater housing for my Nikon 2500. Looks like one option is to upgrade that camera to a 3200, and buy a housing for it. Unfortunately, that is pushing me to something in the mid $400's.
I use a finpix 2650 it takes time for a digital camera to capture a picture and if it's moving the exposure is just too slow and it comes out blurry but if it's coral and not fanning in the breeze it comes out good just look at my photo gallery
I ended up with a NIKON 5900 (I paid about $225) and the Nikon underwater case that was made for that camera (I paid a bit over $200).
Good access to all the controls. Still learning when to switch to macro focus mode. Kept the flash on at all times, and set the camera to not time-out (eats batteries a bit faster, but the battery easily lasts for a snorkelling outing - I bought a spare battery so I could have one charging while I was using the other).
Bit more than I wanted to spend, but I wanted a better (more pixels) digital pocket camera for normal stuff anyway.
Here is a picture of a gobie in a hole in the rock that my son took (Oahu, North Shore):
Sorry for the delay, but I had to find a picture on the computer at home. Here is a school of tangs (with a trumpet fish sneaking along for good measure). Unfortunately, the water wasn't very clear (weather had been a bit rough at times).