To coincide with the release of the CD "In Time: The Best of R.E.M. 1988-2003" on 28 October 2003, the third season episode "Slumber" included only songs by R.E.M.. The album is released on Warner Brothers, the same company that produces this show. It was also a reference to the show's relation to sleep; Chloe makes an offhand reference to the R.E.M. (rapid-eye movement) state of sleep.
During Clark's second encounter with Sarah Conroy, a poster can be seen on the wall above the display case that says 'Emerald Knights,' which is a reference to Green Lantern.
This episode shows that despite his superhuman abilities and physiology, Clark does indeed get tired and needs to sleep. Lana could tell by looking at him that he was tired, and he was unable to will himself to stay awake, unlike Superman in the comics.
All the music in the episode is by the band R.E.M. which is named after "Rapid Eye Movement", a sign of deep sleep.
The Conroys are the second family to move into Lana's old house. In Season Two's "Visage", Clark mentioned new people who have moved into Lana's old house and who have a "little orange cat."