Perhaps there are no normal one-eyed vertebrates. However, invertebrates perhaps are not bound by this; I remember seeing a Superman comic in the early 60s in which Superman’s mermaid friend Lori Lemaris was communicating with a one-eyed octopus.
Granted the writers and artists of Superman comics are not authorities on zoology, are there any normal one-eyed creatures in the animal kingdom (other than insects, microorganisms, and other real tiny creatures)?
Must…resist…urge…to…make…penis…joke…
Darn! Beat me…
Thanks, Colibiri. 
And to the others: If your answer is what I wanted, I’d have posted this in MPSIMS. So there. 
I see that your OP you wanted bigger beasts, but the Cyclops is the biggest animal that I can think of offhand than normally has just one eye.
The origin of the eye in evolution dates to sometime after the origin of bilateral animals became successful. Therefore, one would predict that eyes as one would ordinarily define them would only be found in bilateral animals. This is indeed the case, barring a few anomalies.
Photosensory organs (eyes) appear in animals that are not bilaterally symmetric. Sipunculids, such as Phascolosoma, provide good examples of this. Image forming eyes exist in the invertebrate phyla Mollusca and Arthropoda, which are also in the super-taxon Bilateria.
There is no physiological reason, except for evolution, that cyclopianism should not be common. Bilaterality evolved for various reasons (it was proably adaptive for locomotion) and binocularity merely follwed that.
Planaria, for example have two eye spots. Arachnids have multiple eyes, probably due to reduplication of the basic two in Bilaterians. One could make a strong argument ad reductionem semplicis, for two eyes for stereoscopic vison.
Sipunculans, also called peanut worms, are sea animals. They are bilaterally symmetrical. I also can’t remember anything about them having eyes but it’s rather moot if they’re bilaterally symmetrical.
Since the serious answers have already been given, I’ll throw in my contribution.
Pirates.
Fish.
They only have one eye.
Wrong. Demonstratably wrong.
The only way I can get this is if you’re using some very odd definitions. If you are, please explain them.
Otherwise, as I have said, I can’t see any way around you being wrong.
Huh?
Everyone knows that fish only have one eye, not two.
Otherwise they’d be called fiish.
[sub]sorry, sorry, i’ll be moving right along now[/sub]
D’oh!
No tricky definitions, just one dodgy spelling.
Pretty good.
Only if you have a pretty strange definition of good.
Prsonally, I feel that joke stinks like fiish.
When I was a kid, my neighbor had a Pekingese with one eye.
I think sea urchins only have one eye.
-Ben
I doubt this. Please prove some backup. Starfish have five “eyes,” one at the end of each arm.
I know absolutely nothing about these critters, but why would bilateral symmetry preclude having one eye? One eye in the middle would be symmetric.
Edwino has posited that since eyes evolved after bilateral symmetry monocular organisms will be rare, simply for phylogenetic reasons. Neurodoc stated that sipunculans were not bilaterally symmetrical and yet had evolved eyes, casting into doubt the reasons why monocular animals are rare. Since they are bilaterally symmetrical edwino’s argument stands.
I don’t imagine bilateral symmetry would preclude monocularity, however it would have to be derived from a binocular state, and since binocularity offers so many advatages such a condition would be rare.