I run a scuba diving center and keep several Casio EX-55s with their underwater housing for rental. Surprisingly good results from such a cheap camera, and the housing is so compact and durable I've even taken one snow skiing with me. This model is now superceded but I'd certainly look at their current range. Even with batteries that are over 2 years old I still get over 300 shots per charge, using flash for most and the backlit screen for all. Compare that with the various Canons, Olympus & Sea and Sea, all of which have struggled to go past 50 or 60 exposures per charge. The more times you have to open the case to change the battery the more risk there is of flooding.
5D & 7D (both gripped), 24-105L, 100-400L, 15-85, 50 f1.8, Tamron 28-75, Sigma 12-24, G10, EX-Z55 & U/W housing, A1+10 lenses, tripods, lighting gear, etc. etc.
"I prefer radio to television. The pictures are better"