I get asked this quite a bit so I figured might put it in writing where everyone can see.
My camera right now is a Canon 60D. I use a dicapac bag to protect it from the water.
I had one last summer and got a new one for this summer (on Amazon price is from $60 to $70). You have to be really careful on making sure you close it properly each time.
If you have the funds you can try an ikelite case, they seem safer.
Otherwise check out Brooke Shaden's post she now sometimes uses a point and shoot made for underwater photography. HERE