sssssss (1973)

aka Ssssnake. Hissssss.
"Long live the king."
Dr. Stoner (Strother Martin), who researches into snakes, hires David (Dirk Benedict), as his lab assistant. Little knowning that the doctor's experiment's include a serum to transform a man into a King Cobra, which he plans to test on David.
Understated little creature feature, with a shock ending, that you can see coming from miles away.

attack of the giant leeches (1959)

aka Demons of the Swamp.
"Laugh if you want, but that weren't anything that nature put out there!"
After the town drunk maintains he's seen a giant creature in the swamp, he's laughed at. But then people start disappearing, and they stop laughing. Eventually local Game Warden Steve Benton (Ken Clark) gets wind that somethings up, along with Dr Greyson (Tyler McVey). Will they discover what's eating the locals, and can they defeat them?
Low budget monster flick, featuring Jan Shepard as the inevitable love interest. Produced as a drive-in quickie, this has its moments, and makes for a passable 60 minutes, if you like cheesy creature features.