This is one of my favorite list on Wikipedia: The Worst Movies Ever, which details movies that "have achieved a significant level of infamy through critical and popular consensus as being among the worst films ever made." Oh, yeah!
Dalton Ross of Entertainment Weekly wrote an in-depth yet entertaining article on why Manos The Hands of Fate sucks the big one:
During the conversation, Warren boasted that making a movie wasn't so hard. Anybody could make a movie. Heck, even he could make one. Warren bet Silliphant that he could take a film all the way from conception to completion. Tellingly, the first outline for his master script was written right then and there on napkins. The story was standard B-grade horror — family (husband Michael, wife Margaret, and daughter Debbie) gets lost en route to a vacation and stumbles upon a horrifying fate. Less standard, however, was a half-man, half-goat character named Torgo, or the mysterious cult leader known simply as the Master who walked around sporting a robe with giant red hands on it. Perhaps the film's first sign of ineptitude was the title itself, Manos: The Hands of Fate, which translates a tad redundantly to Hands: The Hands of Fate.