Perfect Guitar Tuner (8 String Drop E = E B E A D G B E) - YouTube
8 string Tenor Guitar mini Strat conversion with color and tuning options (Color: black, Tuning (low to high) for your application: Octave Mandolin unison (GG DD AA EE))
Video - 8-string guitar (thirds tuning talk)
8 String Guitar Tuning Guide | Sweetwater
BLOGoZON No.214 - 8 string (F#BEADGBE) factory tuning C natural octave shapes plus Meshuggah Ibanez M80M