We were able to see Jason and the Argonauts, Twenty Million Miles to Earth (Yay Ymir!), and The Seventh Voyage of Sinbad. You can get a quick overview of these and the other Harryhausen classics that the wonderful people of the Take Up folks ran as part of their Titans. Will. Clash. series at this blog here.
Jason and the Argonauts. This is the classic skeleton fight-scene.
It just doesn't get any more Old School than that!
Talos, the Harpies, the Hydra -- just the Jason and the Argonauts movie alone has some amazingly cool monsters in it that have left an indelible mark on so very many little kids who watched this stuff on late night tv, or whatever. The influence of Harryhausen on OD&D could be a book unto itself. Just compare Talos with the Iron Golem. You can find your way from there.
If you take a good look at the Ymir from Twenty Million Miles to Earth, all it needs is to have more of a beak/less of a snout, and a boney-club on the end of his tail and you've got a very well-done Shen from Empire of the Petal Throne, another Old School game.
What I find kind of weird is that the RPG monster-makers seem to have overlooked the 4-armed snake-lady, guard-dragon, and two-headed roc from The Seventh Voyage of Sinbad. Everyone remembers the cyclopes...you know the guy: he's the one-eyed giant with a horn on his forehead and looks like he's at least partially related to a satyr. That Cyclops is absolutely one of the best versions out there, a real classic.
You can see the 4-armed snake-lady towards the end of this clip:
Now that's a cool spell for a villain, or anyone else to use! Not exactly the best attack in the books, I grant you, but awfully useful for beguiling a local potentate, currying favor, or trying to get a ship weaseled out of the Caliph. Of course, that would require a game in which you were doing that sort of thing from time to time. After watching these movies, why wouldn't you want to run a game like that?
Sure, this stuff might not compare all that favorably against Avatar's 3-D mega-smurfs, and yes, it does look fairly cheesy by current standards, but keep in mind when these movies were produced and that this is still some of the best of the best when it comes to stop-motion-animation. Harryhausen is Old School. And I for one think that is very cool.
EDIT:
In regard to the 4-armed snake-lady mentioned above, I was perhaps too brief and not clear in my intention. I see some serious potential in a spell-crafted entity that has heightened DEX & CHAR, even if it costs them a penalty in say WIS, INT or even STR, especially when that creature serves their master as a potential assassin, concubine or whatever, especially since the spell-caster can have them revert back to a human form later on--possibly with no memory of the perfidious or foul deeds that they might have done in the alternate form. When you add in a hypnotic/charm ability, four arms that might be able to strike or use weapons (probably light ones), and a constriction-attack tail...possibly a bite...you get a lot of utility from this spell and the subsequent critter created by it. Making it so that the subject loses their memories afterwards makes this a sorcerous equivalent to a plastic gun--it'll get places that otherwise you'd never be able to reach. So no, I don't see this as a yuan-ti or a Type V demon. Though, there is a chance that the ritual used to convert this person might have lingering after-effects. There could be a period of time during which stress might trigger a reversion to the serpent-taur form, or in a more wicked variant the ritual might so pollute and taint the victim's cells that they end up spawning what amounts to yuan-ti...but you'd need to call them something else as last time I looked the yuan-ti are not in the SRD. Maybe this ritual is used on male devotees of a cult that summons Type V demons so that they might mate with them and produce demonically-descended heroes and champions for the cult. Hmmmm...that could get interesting. Gross, but interesting from a DM viewpoint.