LokSak. I have used these to keep things dry for years. I use one to keep my XD9sc dry and carried in a cargo pocket of my shorts on every float and raft trip I go on. I swim in the river, jump off cliffs, and generally roughhouse in the river. My gun has never gotten wet yet. They are US Navy approved, and certified waterproof to a depth of 200 ft. for two weeks submersion.
If you are looking for a hard case, then the only thing to get is Pelican Case.