The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Penny is having a go at Sheldon and Leonard, there is a shot of some metal pans with stage lights visible in them. (00:12:30)

The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Sheldon is mentioning about the coffee table having a garage sale, there is a shot of Leonard with all the stagelights reflected in the kettle. (00:06:40)
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Leonard opens the door at the start a yellow tape marker is visible in the centre of the door way. (00:00:40)
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: At the very start, Raj walks over to his seat and a tape marker is visible on the floor. (00:00:05)
Chosen answer: The song is called "Dark as a Dungeon" and was written and first performed by singer-songwriter Merle Travis in 1946. It has been performed by a wide array of artists, including Tennessee Ernie Ford, Harry Belafonte, Dolly Parton, Queens of the Stone Age, Kathy Mattea and Amy Grant. But it was made most famous when it was performed and recorded by Johnny Cash during his concert at Folsom Prison in 1968. According to Wikipedia: "It is a lament about the danger and drudgery of being a coal miner in an Appalachian shaft mine. It has become a rallying song among miners seeking improved working conditions."
Michael Albert