There are a lot of waterproof cases out there, but I think it's safe to say that the RainBallet Waterproof iPhone 4 Case takes the cake.
While other products tend to allow a some leakage, the RainBallet Waterproof iPhone 4 Case will keep the phone dry at all times, even when it's completely submerged underwater. Like every cover, the RainBallet is shock-resistant and protects the phone from scratches. Perhaps the most unique feature is that you can actually take high-quality pictures underwater with this protector on.
While the bulkiness of the RainBallet Waterproof iPhone 4 Case might be a turnoff, it doesn't interfere with sound quality and it does an effective job of protecting the mobile. It's definitely a purchase worth considering.