I love Night of the Demon. The scene you mention at the end, when the monster is revealed is about it's only bad point. Up until then it'd done a great job of suggesting 'something', and so when the Kong-like demon finally arrives it reduces everything down to the level of your average B monster movie. Besides that though, it is great.
Back on the British sf/horror tip, Lifeforce is a real guilty pleasure of mine. Everyone seems to hate it but I can't seem to get enough of it.
http://www.youtube.com/watch?v=G32tVg4Ld6g