Has anyone tried the new (I think) Tech 21 iBand cases yet? Sounds pretty cool. Apparently uses d30 material that is soft then goes hard when you drop your iPhone onto a surface. They also do a hard case version, which looking at the pictures I'm guessing means the back is protected as well.
http://www.tech21.uk.com/products-mobile-iphone1.html
http://www.tech21.uk.com/products-mobile-iphone2.html
http://www.tech21.uk.com/products-mobile-iphone1.html
http://www.tech21.uk.com/products-mobile-iphone2.html