A surprising number of famous songs are actually cover of existing songs. While the originals failed to hit big, the cover versions became big hits.
This video shows you the originals and their more famous covers. Some—such as I Will Always Love You by Whitney Houston—are actually common knowledge, but others really are surprising.
One interesting pick is Cum On Feel the Noize, originally recorded by Slade and then covered by Quiet Riot. As a Brit I’ve only heard the Slade version.
The best covers are those which switch genres. Like Bob Dylan’s Knockin’ on Heaven’s Door, which Guns ‘n’ Roses changed from folk to rock.