This is the first episode to mention Angel Radio.
When talking about finding Anna, Dean says "So I'm girl interrupted..." to Sam. Misha Collins is in the movie Girl, Interrupted (1999).
Anna's hospital ward is Ward 42. In The Hitchhiker's Guide to the Galaxy, the number 42 is "the answer to the ultimate question of life, the universe, and everything."
Anna Williams is the third actress (second chronologically, per the flashback in the episode) to play Ruby. Michelle Hewitt-Williams is the fourth actress to play Ruby, albeit only for a single scene.
In the flashback of Ruby teaching Sam how to exorcise demons, he's wearing the same shirt as when he's recounting the memory to Dean.