Incipio Silicrylic for iPhone 4. It gives you 2 silicon colors in the package. I've got the yellow and black silicon skin. Incase you get bored with the skin you put on. The plastic shell frame also prevents the screen protector from bubbling/peeling/lifting/etc.
Below is a review of it:
First Looks: Incipio Silicrylic for iPhone 4 | iLounge