Warner Home Video official announcement of Season Four DVD and Blu-ray is now on TVShowsOnDVD.com.
The Season Four DVD and Blu-ray will be released on September 1, 2009 and will include:
22 Episodes
The Mythologies of Supernatural: From Heaven to Hell
Creator commentary on 3 key episodes
Extended/Unaired scenes
Gag reel
Source: TVShowsOnDVD.com.