Hmmm... I can do underrated TV serials far more easily, but that doesn't translate to foreign climes anywhere near as easily. For films, I would have to start with:

Pi (1998)- A dark exploration of the nature of man and God
Perfect Dark (2000)- The best film ever inspired by Aliens
Mystery Men (1999)- Hilarous comicbook superhero spoof
Silent Running (1971)- one of the inspirations for Star Wars. If that's not a reason to see it, I don't know what is.
This Is Spinal Tap (1984)- The original mockumentary.
Earth Vs The Flying Saucers (1956)- The finest 1950's B movie ever
Enemy of the State (1998)- An excellent look at the US Intelligence machine
Withnail and I (1987)- Very, very funny
Brazil (1985)- Terry Gilliam does science fiction
Being John Malkovitch (1999)- Probably the most original film of the last decade
The Adventure of Sherlock Holmes' Younger, Smarter Brother (1975)- Gene Wilder and Marty Fields at their best
Killing Zoë (1994)- The best caper movie not made in Britain

These are just based on what people around me seem to be unaware of. They may not be underrated in other parts of the world.

winter"Hard to think of them"mute