I also found http://www.key.co.uk/
have a good range.
The ones I have work great for snorkelling. We took them to mexico, stored room keys, wallet, microfibre towel and other junk in them. Tied 30' of paracord to them and clipped the other end to my shorts leaving the drum to float on the surface and follow us around.
We just jumped in a taxi and went snorkelling wherever we wanted without having to leave stuff on the beach.
I also used them for caches. I now have about 5 locations between 5 - 100 miles away (relatives houses and other non public locations) where I have a sealed cache of some food, money, medicine and clothes etc. I'm using the 41.5 Ltr one for most of my caches.
Maybe I should do a write up on what's inside the caches?