For me, it would definitely be Confessions (movie), and 1 Liter of Tears, cliché as it may be. Confessions was a mind-boggling film with a plot that was, now that I think about it, very unrealistic. But it still ended up staying with me for quite a while, and I couldn't help telling basically every person I met to watch it. The cinematography was also pretty amazing along with the effect of the music. And 1 Liter of Tears does not need to be further talked about. It is just a drama everyone should watch for their own good. It has been 10 years since I've first watched it and it still slips into my mind once in a while.
And I'll just biased-ly add Rurouni Kenshin here, just cause I've been a huge fan of Kenshin for a very very long time and I've seen the films 1832748710 times. :)