The song "Rebel of Babylon" from Beyond Magnetic is a touching (yet still bonecrunching) tribute to Layne Staley
A ninety year old fan wrote to Metallica wanting to meet her favorite band. They immediately visited the elderly fan in her nursing home as soon as they found out.
When Black Sabbath was inducted into the Rock and Roll Hall of Fame in 2006, Metallica, who was so inspired by the band, they played a cover of "Iron Man" and when finished James tells it simply. "Thank you, Black Sabbath! We love you!"