I agree with wakela about the Borg Queen and Darth Vader, and for his reasons.
The cool thing about Sauron was that we never see him, not once, ever, and what he looks like isn't even described by anyone (that I recall; it's been a while since I read LOTR). He's the ultimate example of idea that things are usually scarier when you don't see them. Reading the books, you get this potent yet totally amorphous feeling of dread, like Sauron is malice and lust and hubris, not so much that he has those qualities as that those are the things he's made of. Being in his presence doesn't sound so much like being in front of a big scary guy as being enveloped in this cloud of evil, like the psychic equivalent of mustard gas.
The fact the Tolkien never describes his appearance is masterful. The thing, I think, that makes Samara such a scary monster is that there is nothing you can do to escape her. Once you've seen The Tape, you're in her power. You can become her servant or you can die: There isn't any third option. Some slasher with a knife you can fight, you can defeat. You can check in your closet to see if he's in there. Supernatural baddies always have some weakness that you can use to fight them. Not Samara. Even being nice to her doesn't work. Because Sauron is never described, he maintains that same kind of menace. You can't imagine anyone fighting him or struggling to defeat him. He hasn't got a body, just a presence, once you're in it, you're screwed no how big your sword is.
Hey, it just occurred to me that Sauron putting his essence in the Ring to stave off death is very similar to Voldemort making horcruxes in Harry Potter. In either case, you can kill the villain's body, but his soul is safely stowed away somewhere, waiting to be reborn.
