Have you tried Exolife by Exogear ? The case is pretty good compare with others as i's thinner and it doesn't prevent you from using other headphones due to the casing design ?

Check it out

http://www.exogear.com/products-iphone-4.html

The grip and design is excellent for gaming in my opinion. Mophie is kinda think and bulky while Mili's design feels kinda cheap though ~