Can you name some underrated gems for us to watch?

Boy....this is a loaded question, I'm just going to run through genre's.

Action - Con Air (1997)
Adventure - Vertical Limit (2000)
African American - Roll Bounce (2005)
Animated - Paprika (2006)
Biopic - Love and Mercy (2014)
Childhood drama - Au Revoir Les Enfants(1987)
Childhood comedy - Little Monsters (1989)
Childhood adventure - The Wizard (1989)
Comedy - Drop Dead Gorgeous (1999)
Crime - Le Samurai (1967)
Documentary - A Married Couple (1969)
Epic - The Tin Drum (1979)
Fantasy - Wizards (1977)
Film-Noir - Kiss Me Deadly (1955)
Homosexual - Love and Death on Long Island (1997)
Hollywood - State and Main (2000)
Melodrama - Leave Her to Heaven (1945)
Message - The Contender (2000)
Musical - Leningrad Cowboys Go America (1989)
Mystery - Phenomena (1985)
Religion - Dogma (1999)
Romance - Return to Me (2000)
Satire - Undercover Brother (2002)
Science Fiction - Never Let Me Go (2010)
Superhero - Super (2010)
Thriller - Wages of Fear (1953)
Western - The Salvation (2014)

Horror -

The Black Cat (1934)
The Undying Monster (1942)
Abominable Snowman (1957)
Seance on a Wet Afternoon (1964)
10 Rillington Place (1971)
Psycho II (1983)
House on Haunted Hill (1999)
Inside (2007)
Grave Encounters (2011)

The Swedish TV miniseries, Millenium, aka The Girl with the Dragon Tattoo isn't well-known to American's, so it might be a good topic for you. The Daniel Craig version is good, but the original is better.

The Blockhouse (1973) and The Grey Fox (1982). Both are best seen in a dark movie theatre as they feature scenes set in dimly illuminated interiors. There is only one such scene in the latter (a western), but it is key and not to be missed: the protagonist, Bill Miner, who has recently been released from prison after many years for robbing stagecoaches, watches one of those new-fangled motion pictures. His reaction is priceless.

Nymphomaniac (2013) and Nymphomaniac II (2013) / Lars von Trier

A great one if it hasn't been mentioned yet. A very young Spielberg at his finest -

I hope you like Super 8, it's one of my favorite movies