I've ordered a Dodocase "bookback" for iPhone 4. It seems very nice, and the price is very reasonable.
I like that it lets you lie the phone flat on a table without worries about scratching the lens of the camera, which is normally flush with the glass back.
I only regret that I can't use my Glif with it on. I guess I'll have to find another way to prop up my phone when watching vids on it over lunch.