Same criteria as other lists. This list contains movies that are generally considered to be so horrible, they develop a cult following or become praised for their poor quality.
In no particular order, here are some movies I think should be included:
Santa Claus Conquers the Martians
Every single Ed Wood movie ever made
The Incredible Melting Man
Teenagers from Outer Space
Manos: The Hands of Fate
The Incredibly Strange Creatures Who Stopped Living and Became Mixed-Up Zombies!!?
Whoa there fella. B movies don't have to be abortions.
You have a very poor understanding of what a B movie is.
B movies CAN be competently made and actually be good. Just look at John Carpenter's work.
A bad B movie isn't a "great" B movie, it's just a bad B movie.
All "B movie" means is low budget genre or exploitation film. It doesn't mean HORRIBLE low budget genre or exploitation films, even though there are a lot of those and good ones are definitely in the minority.
But seriously. Invasion of the Body Snatchers, The Terminator, Mad Max, Videodrome, Texas Chainsaw Massacre, Blood Simple, Evil Dead. Those
are B movies, and they're also genuinely good genre films.