The crew of Supernatural inherited the dead tree seen in the cemetery in season 2's episode "Children Shouldn't Play with Dead Things" from The Exorcism of Emily Rose (2005) production. It's also the same dead tree that played prominently in the season 1 episode Scarecrow (2006).
Children Shouldn't Play with Dead Things (1972) was the title of a 1972 zombie movie in which a group of actors lead by their director, Alan, performs a black magic ritual on a island graveyard and causes the dead to rise and kill them all.
When Sam deposits his father's dog tags at his mother's tombstone they read: "Winchester John 306-00-3594 Type - AB Non Religious"
Summer Glau was originally cast as Angela, but had to drop out due to scheduling conflicts. Amara Zaragoza took over at the last minute. Some cable stations, such as TBS and TNT, that later re-aired the episode, still list Summer Glau as playing the deceased "college student" in the program description even though she was replaced by another actress.
The alias Dean uses when he introduces himself to Neil is Alan Stanwyk, which is the name of Tim Matheson's character in the Chevy Chase movie Fletch (1985).