The first Matrix I really liked - very stylish!
Gattica's another thant made a big impression among a sea of largely average and terrible sci films borrowed from the local video shop some years ago! I found it very moving.
Blade Runner is another classic in my book. Serenity, which I already mentioend in connection with Firefly.
And on the Fantasy side of things, the Lord of the Rings trilogy has to stand out for sheer scale, beauty, adventure, romance - it has everything, and all done brilliantly too!
Which makes me think of The Princess Bride, one of my favourite films of all time, whatever genre. It has everything too, with added humour :).
Over to you :)