Johann Sebastian Bach, Well-tempered Clavier BWV 846 - piano score, first 4 bars:
A professional musician told me that one of the defining characteristics of this piece is that during the course of it, the piece "transposes itself" down an octave. This is clear when you compare the first measure with the 32nd measure.
In contrast, here is how most guitar transcriptions, including my own, do it:
Measure 1 and measure 32 are the same octave. There is no transposition, and the guitar version is missing a significant feature of the piece.
A better idea is to start an octave higher. However, this is almost impossible on the guitar. The first problem comes in the 5th measure - you would have to reach to the 17th fret! A nice solution, that in the end has some serendipitous results, is found by transposing the piece down a fifth, and tuning a dropped D.
This is very playable, and at the latter half of the piece it becomes much easier to play, allowing the performer to concentrate on expression, rather than fingering.
It was really cool that my old bike riding friend and guitar teacher Allan Alexander liked this new arrangement enough to include it in his latest book "The Baroque Gig Book for Guitar". Allan's work is meticulous; he improved my fingering and his recording on the accompanying CD completely captures the downward transposition that you formerly only heard in piano versions.
Update May 25, 2010:
You can hear my recording of this on YouTube here.
Update August 2, 2010
Baroque Gig Book For Guitar is available, so I've removed the link to my new score.