I just got my wife an iPhone (3g 8gig). I bought the standard, nothing special, rubber case for it. I didn't have any iPhone screen protectors yet so I had put a generic screen protector on it left over from a previous phone.
Crossing a busy highway to get to the coffee shop, her phone fell out of her purse into the road and oncoming traffic. She turned around just in time to see a car run it over going about 30 miles per hour. She ran over to get it much to her dismay almost completely unblemmished from the event!!!
There are a few scratches where the screen protector doesn't cover but nothing more. In fact, she pulled the screen protector off to check and not a single scratch on it!!!!
Another reason Apple is worth the money and the iPhone rules the land...literally.