I purchased one for my last trip to the Caribbean. It cost me about $10 at the local sporting goods store and held up WONDERFULLY. It had a triple zip-loc type seal and worked great. It didn't have a name brand or anything.
I just did snorkeling and swimming, not diving, so I'm sure it's probably not rated for that.
[This message has been edited by platflyer (edited 08-15-2002).]