Elvis Presley, That’s All Right (1954)
The King recorded That’s All Right during a session for another song. He had been resting when he, Bill Black, and Scotty Moore started jamming to “That’s All Right, Mama” by Arthur Crudup. Sam Phillips heard them and recorded them! On the B-side is “Blue Moon Kentucky”. It now goes for $4,000.

Elvis Presley, That’s All Right (1954)
The Thirteenth Floor Elevators — Reverbaration (Doubt) (1966)
Here is an early recording that featured four songs: “You’re Gonna Miss Me”, “Reveraration (Doubt)”, “Fire Engine”, and “Tried to Hide.” The Thirteenth Floor Elevators made it big as a pioneer of psychedelic rock. Sadly, the band only made four albums. Roky Erickson suffered from paranoid schizophrenia, and it complicated things. He later got treated, and they reunited in 2015. He passed away on May 31, 2019.

The Thirteenth Floor Elevators — Reverberation (Doubt) (1966)