I will be taeching about playing Bach on the harmonica at the SPAH convention this year and would like to second what Doug Tate already said about Bach.
Bach is the musician's musician; if I had to go to an island and bring only one composer to play, that would be Bach.
I will be playing the C minor Double Concerto this season with violinist Ani Kavafian and the Westchester Philharmonic. But lots of Bach works and there are already good transcriptions for flute and oboe and trumpet and guitar that have been made. Look into the violin solo Partitas and the cello Suites. All the flute sonatas work, but I usually transcibe the sharp keys to flat keys. The B minor Suite for flute played in C minor. The A Minor Solo Flute Sonata can be played in c minor.
I use the flat keys so I can play more legato and play all the trills and turns. Often I will use a B harmonica so the b minor flute sonata can be played in c minor and will sound b minor. This does not make the piece easier to play but it does make all the trills possible if you know how to play left-hand trills and spit trills.
If you learn to play Bach, you will keep coming back to the music over and over and never miss the joy of wonderful music. Everytime I finsih a work by Bach, I just want to go back and play it all over again.