For what I do the otterbox defender is a must for my iPhone. With that in mind I contacted otterbox about a defender for the iPhone 4. Got a nice reply stating they are currently working on them just don't have a release date. Here is a link she shared with me.
http://www.otterbox.com/iphone-4-cases-coming-soon
http://www.otterbox.com/iphone-4-cases-coming-soon