(and only one is fan-boy-ish at all, methinks)
Magus (Chrono Trigger)
The music for this guy was one to really set a tone, I thought, and since there is no voice, the BGM kinda feels like it'd fill that void. Instead of running like the rest of the cast, he casually glides... and the scythe...
His history is well-written, and he's an optional character... I think he adds a lot to the game, personally.
Victor Delacroix (Chaos Legion)
The power with which he commands his presense is, to me, amazingly well done. Enigmatic up to the very end. I stole this guy's last name because he's so awesome.
Knuckles (S3)
Knux used to totally look evil... *sigh*
Zorn/Thorn (FF9, for comedy factor, if nothing else)
And last, but certainly not least, my favorite psychopathic annihilation machine, ZIO!, from Phantasy Star 4! (If you haven't played the game, you need to.)
Zio, the head of a church that worships Dark Force, is the driving force for the assembly of the party (and the start of the story itself). While he's not the final boss, he's perhaps the most memorable character in the game (not sure if this is true for other people). His melee attack animation, for example (holds his right hand away from his body, and three bolts of blood-red ANNIHILATION... ahem... magic laser thingies hurl into the sky, only to reappear in the foreground, striking his targeted character.) was an amazingly good visual, at the time, and I still think it's the suavest pseudo-physical-attack EVER!
He's rather difficult to beat, at the point you encounter him, unless you've been levelling.
Zio = Awesome
To the above: Gig is awesome... and you're right, the voice-acting is amazingly well done, right up there with Laharl (D1) and Vyers (Mid-Boss) (D1 and to a lesser extent, D2)
Nessiah is amazingly manipulative... but he's an angel, so it's not like he really had to earn his power (honestly, when I found out what was going on, I was like "Really? An ANGEL? Dude... talk about an uphill battle... >_>")