I gather Battlefield Earth is one of the worst movies ever. I've only seen clips of it but it was excruiating.
The worst acting I've seen in a film is definately in Troll 2:
https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/HyophYBP_w4&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/HyophYBP_w4&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>
well the whole film is bad, terrible.
Another bad film is 'Night Train to Terror'. A really dodgy horror film, that kind of rips off the classic 'Dr Terror's House of Horrors'. It's full of horrible 80's effects that you can't help but love.
For gore, the basketcase film are very bad. They're about the vendetta of a guy who is angered at the seperation of his deformed conjoined twin brother. He keeps the brother in a basket and uses him as a weapon to kill people. Just hearing the description you can tell it's bad. It's full of really graphic gore.
As for the films of Ed Wood. They may be bad, but they're cult classics now. I don't believe most the mediocre films of today will ever be regarded in the same way. As a director he was not grea, but at least he had a vision and he was committed to it.