Any series, any movie of course. I'll get the ball rolling. Star Trek II - the Ceti Alpha ear-slugs, that goes without saying. Star Trek III - those hissing, leathery serpent-things Klingon Commander Kruge fought on the Genesis planet. Star Trek TOS "Operation Annihilate" - the buzzing, croaking, fried-egg brain parasites were heinous enough I wanted Sigourney Weaver to suddenly appear and hose them down with a flamethrower. Star Trek TOS "The Man Trap" - The snouted salt vampire with such a sad look in its pupil-less eyes. Star Trek TOS "Devil in the Dark" - the Horta, which I thought was so bizarrely creative you gotta give it some credit; it looked like a heaping series of pepperoni pizzas somehow blended with heaping piles of those thick-woven afghan-blankets, somehow blended with god knows what else. Star Trek TNG "Conspiracy" - that slimy mama alien festering inside what's-his-name's half-destroyed body, which Picard and Riker were forced to blow to hell. Star Trek VOY several episodes - species 8472 for being the most wildly gonzo-looking alien species I've seen on that series. They looked like something crazy-artist H.R. Giger may have found interesting. No worries, I'm sure I'll think of more later.