I use an otterbox commuter and a brookstone smartphone wallet. I've been a 'naked' guy for every other iPhone I've owned, but this one I just didn't like thinness of it (gasp, blasphemy). With how good the camera is, I also worried about it sitting flat on surfaces and scratching the glass on top of the lens, leading to 'fuzzy' images.
This does make it a lot thicker, but it also replaced my wallet, so that's a wash, if not an improvement.
The brookstone wallet is really snug, but it has a neat little tab on the back that when you pull it, it pushes the phone out. It adds an extra layer of shock protection, carries my DL and 2 CC's and a swiss army tool card (pen, toothpick, tweezers, file, mini screwdrivers and is about as large as my old wallet was. I also don't have to worry about putting my phone in the pocket with keys.