In Leslie Fish's filk song Where, Oh Where, Has Cthulhu Gone, the Great Old Ones pack up and leave Earth, frightened by the invention of the atom bomb (and man's eagerness to use it).
Where, oh where are the Old Ones gone?
Scrambled back to their darkling lands
They have fled with a rare good sense
The lightnings held in human hands
ThisEar Worm about narwhals has a lyric that claims "they stop Cthulhu from eating ye", before showing an octopus-like creature (most likely Cthulhu) attacking a boat and subsequently being impaled by the horn of a narwhal.
The song Intergalactic by the Beastie Boys has a music video that depicts what appears to be a robot made of Erector Set taking on what looks like Cthulhu. Erector Bot wins by punching the Eldest One into some power lines.
In the Charlie Daniels Band song "The Devil Went Down to Georgia", Satan challenges a violinist named Johnny to a fiddle-playing competition. A solid-gold fiddle against Johnny's soul. Johnny takes the bet, warning the Devil, "I'm the best that's ever been." Once they play, the Devil doesn't even need to be told that he lost, handing over the gold fiddle without a word. Johnny responds with one of the most badass lyrics, ever. Ever. "Just come on back if you ever want to try again. I told you once, you son of a bitch, I'm the best that's ever been." (it appears in Guitar Hero III as BGM to a guitar-battle with Lou)
The Devil tries again in the follow-up song "The Devil Comes Back To Georgia" after Johnny has married and has at least one kid. Predictably, Johnny beats him again.
The GWAR concept album "Beyond Hell" ends with GWAR threatening to "kick The Devil's ass" and succeeding.
Jimi Hendrix went to a Cream concert in the 1960's and asked to jam with the band. Already a bit brave to do, this man walked up there, and played through a song that Eric Clapton himself decided was too hard to play. Imagine how that would feel for Clapton to be outdone by a guy in the audience.
