SPOILER: Several references throughout his appearances on the series point toward the character Rufus Turner (played by Steven Williams) being Jewish. He makes jokes about Hanukkah and keeping kosher, and most significantly, when he dies, the Winchester brothers and Bobby give him a funeral in a Jewish cemetery and discuss his level of Jewish ritual observance (or lack thereof). Although the funerals for previous hunters had included a ceremonial funeral pyre, the show makes a point of showing that Rufus gets buried without cremation (since cremation is against Jewish tradition).
There is a particular clock that shows up in almost every episode.
An important aspect of the show's music is classic rock, most of which comes from creator Eric Kripke's own record collection, although one of his favorite bands - Led Zeppelin - has always been too expensive to license.
The role of Ruby was written for Kristen Bell. But she turned it down, Katie Cassidy was cast instead.
Jim Beaver's character (Bobby) was only supposed to make a one-time appearance.
While it maybe coincidental the choice of the name Winchester for the family is interesting. There is a...
Originally Jensen Ackles auditioned for the role of Sam Winchester. When Jared Padalecki came in and read for Sam a slight recasting was done. Producers called Jensen and asked if he'd rather use his charm for Dean, saying he was the Han Solo character of the duo and what kid didn't grow up wanting to be Han Solo? Jensen accepted. It became known that he was previously interested in that role, because Dean was funny.
Riverview Hospital, a large mental health facility used as the main set in the season 1 episode Asylum, has also substituted for a prison, a regular hospital, and an...
Many of the episodes are based on existing legends, myths, and ghost stories. For example the episode "Crossroads" is based in part on the legend of Robert Johnson - who in turn borrowed it from another Blues singer.
Many episodes are either named after movies ("Children Shouldn't Play with Dead Things", "The Usual Suspects", "I Know What You Did Last Summer") or classic rock songs ("In My Time of Dying", "Born Under a Bad Sign", "What is and What Should Never Be", "Sympathy For The Devil", "When The Levee Breaks").
Early on in the series, Dean's cell number is given, and for a while the studio had it set up so that anyone dialing the number would hear Jensen Ackles reading the message: "This is Dean Winchester. If this is an emergency, leave a message. If you are calling about 11-2-83, page me with your coordinates." The number is 1-866-907-3235.
The car Sam and Dean drive is a 1967 Chevrolet Impala, which has been nicknamed the Metallicar by fans of the show. The show uses five black Impalas. Dean has nicknamed the car "Baby".