I whitewater kayak so I see lots of guys with cameras that need to be able to take a swim and must be 100% waterproof.
For casual use you could try this
http://www.rei.com/product/752136 They seem decent but I wouldnt rely on it 100% as I have heard some complaints about leaks. You could also go with a pelican box
http://www.rei.com/product/723937 if you are sure you will be using the camera on dry land but need to transport it over water. (this is what most kayakers do as they typically have SLR types of cameras with lenses.) I would trust this option 100% and would be the best bet if you have expensive equipment and want to protect it from both water and bumps.
For myself I have a Canon enclosure for my sd550 that can be used for diving.
http://www.amazon.com/Canon-WP-DC80-Waterproof-PowerShot-SD550/dp/B000B674C0