I don't usually write about music. The whole point of music is that it's different from writing. Like a joke, the moment you start explaining it the thing doesn't work. And yet...
Some songs are very like other songs. Famously, the Hammond organ bit of Procul Harum's “A Whiter Shader of Pale” was inspired by J.S. Bach (see this archived page for much learned discussion on what and to what extent).
“La Bamba” by Richie Valens is pretty much the same tune as “Twist and Shout”, while there's more than a little of “My Way” in Bowie's “Life on Mars” – as this superb version shows. (See The Ukulele Orchestra of Great Britain website for more splendiditude.)
I also keep hearing TV themes in pop tunes. The NME has spotted that Muse's “Uprising” is a lot like Doctor Who. But S Club 7's “Reach for the Sky” is the theme tune to Duck Tales and Alexander O'Neal's “Criticize” is the theme tune to Duckula.
And then there are the lyrics. Ronan Keating's “When You Say Nothing At All” has the same message for the ladies as Joe Dolce's “Shaddap You Face”.