"Houses of the Holy" is the name of a Led Zeppelin album.
Dean, speaking of Zach the drunken killer, says "Roma Downey made him do it". For 9 seasons Roma Downey played the angel in the CBS series Touched by an Angel (1994).
On "Houses of the Holy" one of the songs on the album is "No Quarter" and later on, Dean runs out of quarters when using the Magic Fingers.
It is shown in this episode that Dean does not believe in angels and believes they don't exist. In season 4, Dean befriends an angel named Castiel and they become best friends over the course of the series.
When Dean is using the Magic Fingers, it shows a quick glimpse of his music player. It reads "led zeplin- kashmir" Kashmir is on the 1975 album "Physical Graffiti"