There is an excellent article on slate.com about a record that Todd Rundgren did called "A Capella," which is, naturally, songs without instruments. Here's a little something:
With all the predictable approbation Medúlla [Bjorks new record] has received, it's worth noting that Todd Rundgren performed the same "all vocals, all the time" experiment on his album A Cappella in 1985. The mid-'80s were an antediluvian era for recording, yet Rundgren, using time-honored overdub techniques, crude sample machines, and nothing but his voice, created a lush, gorgeous record that rivals Medúlla for its mad-scientist invention and ambition.
I'm pretty sure that Todd Rundgren is advanced, but I don't know quite enough about his work to say for sure.