I love Magpul DAKA pouches. They are built like a brick shithouse, work well, and look great. However, they are expensive and because they are zipped, they are not 100% waterproof.
If you need something to stay absolutely dry when submerged, similar functionality otherwise, and a lower cost solution… well, check out these resealable Stasher silicone bags. While they might not look the business, there is no arguing their functionality.
And if money is burning a hole in your pocket, but you still need something absolutely submergible, Nite Ize recently introduced their new RunOff Waterproof Pockets in a number of different sizes and colors. These things are priced similar to the DAKAs, but use a different kind of zip system that allows them to be completely waterproof.
I haven’t used or seen these, but initial reviews are really good.