The Most Influential Sci Fi Movie according to me are:

The Thing (1982)
The Terminator (1984)
District 9 (2009)
Twelve Monkeys (1995)
V for Vendetta (2006)
Stalker (1979)
Nausicaä of the Valley of the Wind (1984)
The War Game (1965)
Star Trek (2009)
Avatar (2009)
The Truman Show (1998)