I have stumbled upon an interesting gadget designed for especially iPhone gaming.
This silicone grip as you see in the photo claims that it will give more comfort to play iPhone games. Built-in charger slot lets your device to charge while you play. Silicone sleeves can be used as stand alone protection when not playing games.
Whether it is so useful or not but surely quite expensive. Available at Marware $50 for iPhone users who are really interested in.