From SF Signal comes a link to the best science fiction and other related films as picked by authors such as Robert Bloch, Arthur C. Clarke, and Frederik Pohl. The only downside is that the list is from 1994; as such, it's heavily weighted with films from the middle of the 20th century while more recent films receive few mentions.

A few post-1994 SF films I'd add to the list include Gattaca (1997), Children of Men (2006), Twelve Monkeys (1995), and most importantly, Alex Proyas's masterpiece Dark City (1998).