Night of the Lepus 4 words: Giant. Killer. BUNNY RABBITS!
More Godzilla movies I mean, COME ON!
Any and all movies based on video games
The Marvelous Land of Oz A super cheap adaptation of the of 2nd Oz book, made by the director of Santa and the Ice Cream Bunny & its inserts and starring his mush mouthed son.
Gappa, the Tri-Amphibian Monster In a sub-genre filled with silliness (Japanese Giant Monsters Movies), this one takes the cake!
Something Animated There are a lot of mediocre/bad cartoon movies out there!
Super Monster Gamera Our old buddy teams up (though I use the term loosely) with some superheroines (I use the term even more loosely) to fight a space pirate who attacks Earth with stock footage from all the previous Gamera movies (and the anime Galaxy Express 999) and stole a Star Destroyer.
Bella Lugosi meets a Brooklyn Gorilla ...and a couple of guys who rip off Dean Martin and Jerry Lewis
TNT Jackson and/or Blackbelt Jones While I'm not sure how they'd feel about the "Blaxploitation" part, they could do a lot with the extra silly kung-fu action.
Red Riding Hood and the Monsters AKA Red Riding Hood Meets Tom Thumb A Mexican kids movie from the same people who gave us Santa Claus...
Yog, the Monster Outer Space AKA Space Amoeba A Kaiju movie that features a lobster being called a crab, a squid being called an octopus, cartoon bats, toy dolphins, and people turning into dolls when they fall victim to the monsters.
Flight of the Lost Balloon An adventure movie featuring (among other things) obvious mat outlines, vulture puppets, short gorillas, the world's most shallow lake, and an obviously evil villain one can't believe anyone would trust.
The Legend of Galgameth A kids fantasy that plays like a live action version of Pokémon, featuring laughable effects, a villain you know is evil the moment you see him, an Asian played by a white guy, and a hero who needs other people to do everything for him.
The Land of Faraway A fantasy movie with a kid riding in a giant's beard and a villain who makes lightning flash whenever someone says his name. Featuring Christopher Lee and a very young Christian Bale.
Infra-Man A Hong-Kong take on Japanese super heroes that plays like a very busy, very crowded episode of Ultra-Man or a one-man show of Power Rangers that makes "Prince of Space" look Oscar worthy The Greatest Plot Not only does it feature some silly kung-fu (flying guillotines that look like weaponized sombreros, a woman trying to towel slap people to death, and a contraption straight out of the Legend of Zelda), but over the top melodrama makes it like a very action packed soap opera! Hercules vs, the Hydra AKA the Love of Hercules Among the many highlights they could work with are Hercules getting over his wife's murder in record time, a barely mobile hydra, and men being turned into fakey trees.
Rifftrax, which is the same people just not in MST3K character did Night of the Lepus, and as expected it's damn funny!
I'd love to see them do more Godzilla too but I've heard they caught hell from Toho studios for just doing the ones they did, which is a shame. Gamera is owned by a different studio so maybe they'd have more luck going after them.
Warning From Space would be a great one for them to pick on too, Rifftrax did it but it was a couple of annoying British guys and not the MST3K crew.
Showing my age here, but I saw that one in the theaters as a very little kid. It would make for a GREAT MST3K ep!
For some reason, I always thought The Black Hole would make for a good MST ep, too. I'm actually sort of fond of the movie, but it has some serious riffing opportunities, too.