Nthing the Casio G'zOne. I've had one of the older ones for four years now - I keep refusing to upgrade.

I worked as a canoe guide for awhile, and at one point dropped the phone into the water while disembarking from a canoe - into the muddy, nasty, stirred up water of the boat launch. I couldn't see it through the silt at all. By my good fortune, a friend of mine called a few seconds later. The thing lit up like a Christmas tree and began to ring underwater. I fished it out, dried it on my shirt, and answered the call. Worked perfectly, no problems whatsoever.

Hopefully the newer ones are keeping up the quality!