Does anyone know which Arranger has the best implementation of vocal harmonizing? I'm afraid my old SK76 didn't have that built in and required an add-on. Since then, it seems that every arranger has this. Which begs the question.........who is the best?

If you only use the left hand section to trigger the harmonies, AND you use the auto arranger all the time then:
psr 2000 (sounds better than average)
psr 9000 (best mixer section w/ effects)
9000 pro (same here)
X1(not too bad at right hand harmony either)
XD9(same)
SD1 (same)
PA80 (weakest in the lot)

Forget the psr740
Forget ANYthing made by Technics
psr8000 was decent, but fewer voices

Best bet is Yamaha, then Ketron, then Korg
In that order.
(I've had THEM ALL)