TVShowsOnDVD.com has the rear artwork of Supernatural Season Four Blu-ray.
Season Four DVD and Blu-ray will be released on September 1, 2009 and will include:
* Season Four's 22 Episodes
* The Mythologies of Supernatural: From Heaven to Hell – Three sections featurette gallery bridging Heaven, Purgatory and Hell to examine key methological precepts
* Commentary on 3 Key Episodes by Executive Producers and writers
* Extended/Unaired scenes
* Gag Reel
Source: TVShowsOnDVD.com.