A TV Guide Channel special.
A TV Guide Channel special, 25 Things You Didn't Know About Supernatural TV, will air on Sunday, March 26th at 8pm/ET/PT. Both Jensen Ackles and Jared Padalecki will be on it, as will Eric Kripke, Supernatural's creator.
Other shows on the special are Ghost Whisperer, Medium and Smallville.
Source: The Watercooler, TV Guide