Star Wars (even at 5 the original blew me away - saw it 19 times in the theaters)
Lord of the Rings (effects as revolutionary as the original Star Wars, just barely surpasses the original films as the best "trilogy" of all time)
War of the Worlds (both of them were impressive visually - although I think the original was better overall)
Independence Day (amazing mass destruction scenes, great overall effects)
Day after Tomorrow (movie stunk, but it had the same great effects crew as ID4)
Star Trek - Nemesis (love the climactic head-on ramming of the ships, although not as good as First Contact over-all)
Men in Black (great story, great aliens)
Farscape - The Peacekeeper Wars (yeah, it's a TV movie - but it blows away most of the other sci-fi stuff made in the past 10 years, and it was an extremely worthy ending to my all-time favorite Sci-Fi series)
Serenity (the movie that wrapped up the story of one of the other all-time great sci-fi shows that was cancelled far too early - Firefly)
Spiderman (one of the very few movies that greatly surpassed the hype around it, and considering he was always was my favorite super-hero that says a lot

)
The Matrix (one of the most original and visually stunning movies - too bad they didn't make any decent sequels...)
X-Men - both films (one of the few times where the second movie is as good if not better than the first [BAMF!] - my other favorite comic heros growing up, too bad the other films, like Hulk and Fantastic 4, weren't up to this level)
I-Robot (Will Smith seems to know how to pick some great movies, and the robots were just perfectly believable along with most of the other effects)