Not exactly what Czarivey had in mind but somewhat related (and especially to Sfar's comment)- David Hidalgo's accordion on Dylan's "Together Through Life" defines the sound of that recording and really makes the entire album for me. Props to accordion in roots music, at least.
Why not accordion ?
To my point of view it's one of the most universal solo instruments, but not widely accepted in any classical or jazz orchestras or bands. It's also sophisticated. I'd say extremely sophisticated. In order to deliver smooth and artistic sound it may require long and extensive practice to handle bellows and position your hands properly. In addition there are two button boards that can deliver sophisticated polyphonic parts that can create an impression of small band inside one instrument. You can also count on fingers great accordionists while you can have an endless list of great guitarists or saxophonists.