Ray Harryhausen is a stop-motion-animation wizard who is widely regarded as the master of old-school special effects. Harryhausen called his method of animating small models of monsters and superimposing them into live action scenes "Dynamation," and it was used to great effect in such movies as The Seventh Voyage of Sinbad (1958) and Jason and the Argonauts (1963).
I'll never forget the first time I saw the rousing and meticulously choreographed skeleton fight in Jason, in which a team of seven undead creatures spawned from a hydra's teeth are acrobatically knocked, flipped, and stabbed out of commission by Jason and his cohorts, or the gray-skinned, 20-foot-tall Cyclops who gets seriously pissed off when Sinbad and his crew impale him with spears.
This website has short clips of the monsters from most of Harryhausen's movies.
Link (Thanks, Joe Alterio!)