If I was going to read on the beach then I'd get the TrendyDigital case/bag that Egham linked to. It looks nice and secure.
However, I'd still probably just get a pBook when reading on the beach or by the pool. Not because I'm worried about it getting wet but more because I don't have to worry about it if I want to get up or walk around without lugging it around. If my pBook gets stolen or lost then it is mildly annoying but not a major issue however my Kindle getting stolen or lost is quite a bit more annoying
