I'm a professional UW photographer. The Olympic TG-5 seems to be the camera of choice for a solid entry-level camera. You will need a housing to go to 100'. The big advantage of the TG-5 is that it shoots RAW. If you can find a good used TG-4, they're almost the same, except in low-light performance.
If you can manage it, SERIOUSLY consider using a strobe or (groan) video light. At those depths, your pics will seriously lack colour without it.
My four rules for successful UW photography (I teach this shit, so consider this free advice)
1) O-rings first, beer second
2) Get close
3) Stay low
4) Now get closer
I use dSLRs, and have no first-hand experience with this camera, but they're popular
Follow me on Twitter to see some of my work. @DougalShort