Hurray! You can pre-order the Supernatural Season Five DVD on Amazon.
I don't know the release date, but I assume it will be at the end of August or September, it usually comes out a few weeks before the start of the new season.
According to Supernatural Fans Online, there should be a commentary by Eric Kripke, Robert Singer and Ben Edlund on The End. You will also see unaired scene from The Real Ghostbusters.
Stay tuned for more details on the DVD.