I always like making lists, but I've a feeling this will be my least original one.
In order of recolection:
1. Lord of the Rings
2. Oldboy
3. Requiem for a Dream
4. Spirited Away
5. X-Men 2
6. The Incredibles
7. No Country for Old Men
8. Children of Men
9. Kill Bill
10. American Psycho (I actually like this one more and more every time I watch it)
Creeping up the list: The Fountain, There Will Be Blood, Ratatouille, Casino Royale, Brick, Day Watch, Finding Nemo, The Host, Pan's Labyrinth, Munich and Zodiac
Fallen off the list, but still very fond: City of God, Battle Royale, Revenge of the Sith, Hulk, United 93, Lady Vengeance, Happiness of the Katakuris, Ichi The Killer, Royale Tennenbaums, Eternal Sunshine,
Obviously I need to watch more modern foreign films, the majority of my favourites in that area came out before 2000. Welcome to Dongmakgol has been on my 'need to see' list since one of the DVDActive writers reviewed it upon its initial Korean release.