I have a three that are particularly awesomely terrrible and/or baffling.
Pieces- I think this 80's horror film is Italian but everyone is dubbed over with English voices. It's just hilarious, insane and so very bad in the best way.
Flesh for Frankenstein- This film is just so perplexing in almost every way. It stars a young Udo Kier and a host of actors whose nationalities are unclear. The more I think about this film the more I think that it's perfect for HDTGM. It's terrible but it's also entertaining, with such excellent lines as "To know life, you must fuck death!". A Frankenstein story that defies logic in the best ways.
Hausu- Japanese horror film about a motley crew of teenage girls whose names describe their character (Nice girl= Angel. Fat GIrl= Mac) who get eaten/killed/maimed in a series of crazy ways. I don't want to ruin anything because it's a lot of fun but a scene where a piano eats a girl is particularly good.
