E.T. The Extra-Terrestrial
Jimmy Neutron: Boy Genius
The Iron Giant
I've never cared for E.T., but I liked Star Wars and The Iron Giant. That makes 3 of the 7 I've seen, and my kids only saw the 2 of those that I liked. Most of the ones on the above list weren't around when we were picking out movies to watch with the kids, and we made very different choices about the SF movies we thought were worth sharing.....
In addition to Star Wars and The Iron Giant (and not counting monster movies or fantasy) our suggested 7 would be
2001: A Space Odyssey
The Day the Earth Stood Still
The War of the Worlds
The Time Machine (the early one)
The Planet of the Apes (Charlton Heston's version)
Others we liked for the kids were The Last Starfighter and the 2nd Star Trek movie -The Wrath of Khan.