I came across the waterproof cases from Griffin at CES 2013 in January. Being a mainstream brand that sells in big quantity they seem a little better priced than some options.

http://www.griffintechnology.com/survivor/waterproof 
http://store.griffintechnology.com/survivor-waterproof-case-for-iphone-5

Unfortunately I didn't get a sample to try but had a quick play with one and it seemed good.