Led Zeppelin's version of "Babe, I'm Gonna Leave You" from their 1969 debut album (written by Anne Bredon and discovered by Page and Plant on Joan Baez in Concert, Part One from 1962) is very interesting. Musically, it provides an excellent cross-section of the Led Zeppelin sound - the folk and blues influences, the acoustic and electric guitars, the dynamic ranges of all four members - it's all there. It also gives a fine example of how they put as much effort (and originality, strange as it may sound) into their versions of non-original material as they did into their own. Listen to the two versions (they're on YouTube), and you'll hear what I mean.

Their treatment of the lyric is also worth noting, because the protagonist is shown struggling with a decision, seeming to make up his mind, only to reverse it shortly thereafter. Some commentators have credited Shakespeare as being the first artist to show characters doing this - to literally show characters thinking during a story. (Before him, characters spoke in a style that is best described as declamatory - in other words, they simply announced their situation and/or mindset directly, with little or no second thought. Come to think of it, there are still plenty of stories in books and on film told that way. And although this style may be superficially entertaining, there are two problems with it: 1. It's unrealistic, because it's not the way people are. 2. It's boring, because it leaves the audience with nothing to think about.) Back to the song. My main point in all of this is that the song is actually the reverse of the common situation - on the surface, it's a simple story, but it isn't really, because it shows a human mind at work.