I have used several of the waterproof cameras and some P&S models in underwater housings. The housings work well and will give you better quality with a G12 or something like that but they are big and bulky, not convenient for carrying in a kayak and such. Unless you are scuba diving greater than 30 feet deep or need the longer zoom range, I would not go this route.
The Olympus models do not do that well in low light (lots of noise.) The Pentax models do not have image stabilization (needed for shooting from the kayak.) Fuji, Casio, and Sony do not have the quality of Canon and Panasonic in my opinion.
I chose the Canon D10 because it has a larger aperture which means faster shutter speeds and less image blur when shooting from the kayak. I like the Canon color a little better than the Panasonic.
The Panasonic TS2 has a longer zoom range, smaller form factor and shoots HD video so you may choose it if these things are important to you. They have just announced a new model, TS3 but it is not in stores yet.
You can see many photos taken with the canon D10 at my website: