Fantasy
1) The Nightwatch: An awesome movie that very few people have heard of and even less have seen. If you see this movie you will not be disappointed good graphics, storyline, and characters, though it can be a bit confusing at points.
2)The Incredibles (i dont think this counts as fantasy but whatever)
3) Lord of the Rings
4) Edward Scissorhands: A movie featuring Johnny Depp before he got really famous
5) Groundhog Day: A classic movie.
6) Monty Pyhton and the Holy Grail. 2 words "Killer Rabbit".

Sci-fi
1) Back to the Future series: I cant believe no one has mentioned any of these movies yet.
2) Soylent Green: A classic that has been alueded to in numerous other movies and shows.
3) Jurassic Park (the 1st one)
4) Bill and Ted's Excellent Adventure: see Keanu Reeves work before The Matrix.
5) Donny Darko: simply put this is a cult classic.