This is both unusual and beautiful: 欽聖 ChinSheng playing a Baritone Guitar, and I think the tuning here is A D G C E A (starting from low to high strings-there are other typical tunings).
UPDATE: I got a reply to my question about the tuning from Riverside Live Session: “The tuning is A E C G D A. The third and fourth strings are restrung with high octave strings.” =D
Last time I brought my own guitar in for repair, I had the chance to try a baritone guitar, the deep sound is so impressive! Would make a wonderful blend in an acoustic duo. =D
You can read about him and hear 3 songs at his iNDIEVOX page.
ChinSheng facebook. I just noticed if you scroll down the page a bit, he explains the tunings and the instrument. (similar to the wiki link above)