I put movie in all caps above because I wish to distinguish between persons who watched at least one of the movies before delving into the work of the Greater Perfesser, JRR Tolkien. Watching Fellowship and its sequels, what sort of creature did you take Sauron to be?
I thought he was a human, like Sarumon. Then I guessed he turned into some sort of Eye, because that’s what you see “die” at the end of ROTK. 
What was he?
A “satan-ish” one.
I thought he was THE all powerful sorcerer. Who, like Voldermort, was able to retain his essence even after his body was destroyed.
I’ll spoiler-space it in case anybody wants to vote without being, ah, spoiled.
You’re right that Sauron was the same sort of being as Saruman (and Gandalf for that matter), but wrong to think of any of them as human. In Tolkien’s legendarium, they are what is known as Maiar (singular, Maia), which are basically lesser angels who existed before the material world was created and entered with the greater angels (Valar, singular Vala) to shape the Earth according to the design of Eru, whom we might as well call God. Sauron was a servant of the first Dark Lord, Morgoth, a Vala who rebelled against Eru. Six or seven thousand years before Frodo’s time, Morgoth got his ass righteously kicked and was thrown into the Void, completely outside the physical world. Sauron, his chief lieutenant, was given the chance to repent but either only pretended to do so or could not bear the humiliation, and so went into business for his ownself.
I think for the sake of the little bit of good in my soul I have to pretend you did not compare Sauron to Voldemort.
Okay, you thought Sauron was a sorcerer; did you think he was an Elf or a human?
From the movie I did think he was a powerful human sorcerer, basically Saruman x eleventyone. The scene in the beginning has him with his helm and armor, so I assumed he was not always an evil eyeball.
A particularly clever hyper intelligent pan dimensional being.
(Actually, I read the stories as JRRT was writing them, so my post is null and I didn’t vote.)
Where’s the “humanoid pterodactyl” option? (i kid, i kid)
To expand on Skald’s spoiler,
[spoiler]The answer choice “a Balrog” would also be largely correct, since the Balrogs were also maiar. Of course, Sauron was much higher-ranking than any of them, but he was basically the same class of entity.
For a complete list of the Ainur (collective term for the Valar and Maiar) who have any relevance to Lord of the Rings:
Manwe is the King of the Valar. He’s never directly referenced in LotR, but he has strong associations with the Great Eagles.
Elbereth (aka Varda, and given the title Gilthoniel, “Star-Kindler”) is Manwe’s wife, Queen of the Valar, and is highly revered by the Elves. They sing some songs about her in both the book and the movies.
Orome, the huntsman of the Valar, is briefly mentioned in one of the Rohirrim poems in the book. I don’t remember this being in the movie.
Gandalf, Saruman, Radagast, and the other two wizards (unnamed in LotR, but elsewhere given the names “Allatar” and “Pallando”) are all Maiar.
The Balrog and Sauron are also Maiar.
The drivers of the Sun and the Moon are both Maiar. Arien, the driver of the Sun, was in origin actually very similar to the Balrog, but was the one fire-spirit who didn’t go bad.
Melian was a Maia who long ago fell in love with an Elf, and is an ancestress of both Aragorn’s line and of many of the significant elves in the story (including Elrond).
Some will argue that the great dragons were embodiments of Maiar, but this is debatable.
Some will say that Tom Bombadil is a Maia, but this is even more debatable. It’s probably safest to just say that Bombadil is a unique being in a category by himself.
Ungoliant and her descendant Shelob are definitely not Ainur. What they are is somewhat vague in the finished works, but they seem to fit in the category of “fey”, described in some of the unfinished works such as The Book of Lost Tales.[/spoiler]
Huh, I guess I expanded a bit more than I thought, there.
I’m gonna ruin Chronos’s spoiler:
Where are you getting that Arien was the sole fire-spirit who didn’t go bad? I’m not contesting, just wondering.
Yes, Aragorn married his great-many-times-over aunt. 
That is why “Arkansas” was named after him.
I’d debate that very strongly. But first I will gather ammunition.
My god, man, do you know what horrors you are unleashing?
I don’t have my copy of Silmarillion at hand, but it’s hard to imagine that Ungoliant was not a Maia. Or at least I thought so until I wrote that sentence, when it occurred to me that she mated somehow with mortal creatures. Since in Tolkien’s ultimate conception no Maia but Melian ever reproduced, I must concede that you’re right.
Damn it.
I chose “evil elf” because he’s so tall and scary. And everyone knows elves are small, cute, live in trees, and make fudgestripe cookies; the correct deduction would be an evil elf, because he’s compensating for his inherent cuteness and ability to weild huge vats of molten fudge with all that scary, pointy armor by using stilts and growing a goatee.
I’m kinda in the mood for some cookies now.
Damn. I even read the books, and had no idea.
Still though, cookies… TEMPT ME NO FURTHER!
I still have 17 of the perfect cookies from this old thread. I’ll send you one for a suitable fee.
Anyway, persons who have only read THE SINGLE GODDAMN BOOK THAT IS GODDAMN LORD OF THE RINGS but is sometimes referred to as a trilogy by Tooks, Etruscans, and other madmen might reasonably be unsure of Sauron’s origin and species; I don’t think the word “Maiar” ever appears, and certainly even Gandalf’s true nature is only hinted it.
Elrond was his great, etc, uncle, but Arwen was a cousin, not an aunt.
:: tests balance of throwing axe ::
What have I told you about bothering me with facts?
::Looks at Skald’s post::
::Looks at bookshelf::
::Looks at post again::
::Looks at bookshelf again. Counts number of Lord Of The Rings books on said bookshelf::
::checks meds::
::checks birth certificate::
Something’s not adding up here.
Okay, leave that be for now. It looked like in the movie that the Balrog had wings. Is that accurate?
<stands well back to watch the conflagration>
Some sort of humanoid. I mean, his arm got cut off and everything. I guess I assumed he was pretty similar to the Nazgul, but more fleshy.
It was written as a single book, but due to the WWII paper shortages and marketing demands, it was published as a trilogy. Although, if memory serves, Tolkein broke it up into six parts when asked to break it up, which were then condensed to three. So one could reasonably refer to it as a book, a trilogy, or a sexology (er, 6-part series).
And having read almost all of the books before having seeing the movies, I still thought that Sauron was an otherwordly being, type unspecified, and that Gandalf was human, until reading threads on the SDMB about the subject.
EDIT: So if Gandalf the Grey and Saruman the White are non-human, what does that make Radgast the Brown?