While the Beatles always had George Martin around to clean up their act, the Rolling Stones had Andrew Loog Oldham to coarsen theirs.

'Let's Get It On' is a classic Motown single, endlessly repeatable and always enjoyable.

Elton John can be a master of the sleight of hand. The arrangements make it seem like there are substantial melodies underneath the tracks - but almost nothing demands repeated listenings. Similarly, he always sounds like he's singing up a storm, but his voice glosses over the material, reducing most things to an uninteresting sameness.

Joni Mitchell seems destined to remain in a state of permanent dissatisfaction - always knowing what she would like to do, always more depressed when it's done.

When the Beatles cut old rock n' roll, they were recording music still in their performing repertoire, and besides, they never thought of the music as old.

The title song of David Bowie's 'Young Americans' is one of his handful of classics, a bizarre mixture of social comment, run-on lyric style, English pop and American soul.

The Beatles did their best cover work on Little Richard's 'Long Tall Sally' and music influenced by Richard, such as Larry Williams's 'Dizzy Miss Lizzie.