Suggestions for quality non mainstream Sci Fi movies

I  know the FAQ suggests we dont talk about "list of my favourite
movies", but I have a request..

Every now and then, one gets to see a lesser known gem of a movie
(like "The Quiet Earth" for instance. This movies ca be either old and
forgotten, or just slipped under the radar. How about other
suggestions in this vein? It would help the youngsters out there
too...

I would offer for a starter...


The Quiet Earth (obviously)
The Stone Tapes
Night of the Big Heat
Reptilicus
Liquid Sky
The Changes (BBC kids prog)
The Hidden (not that unknown I admit)
Street Trash
Frankenfish (ok, for the laugh factor)
X the Unknown
The Trollenberg Terror
Tomorow I will be Scalding My Self With Tea (all copies lost I fear)