Alright, here's my tentative list, not ranked:
- Inglourious Basterds: enormously entertaining, my favorite QT flick (and I believe the one with the most substance), fantastic performance from Christoph Waltz as one of the most memorable movie villains I've ever seen, a fascinating study of film violence and a passionate love letter to cinema itself.
- The Dark Knight: to me TDK is pretty important because it marks the culmination of all the comic book movies that came before it, it took the genre and pushed it to the boundary, making it a movie that is extremely entertaining, but also something to take seriously, tackling a few weighty themes and moral issues. In my opinion, this is a nearly perfect Batman film with a flawless and memorable performance from Heath Ledger.
- No Country for Old Men: I wish the Coen brothers would make more movies like this. Don't get me wrong, I like their zany, kooky, crime comedies and so forth, but I felt like they harnessed their considerable talent and focused it in making this movie. This film has tension that I've not seen in any other movie, with yet another frightening and memorable villain, played by Javier Bardem.
- The Diving Bell and the Butterfly: a deeply touching film that takes you straight into the mind of the protagonist as he struggles with a situation that most of us would find unbearable. Reminds us of the power of the mind, the imagination and the will to live and find meaning in the face of tragedy.
- City of God: one of the best "gangster" films, if you want to label it as that. It opens the viewer's eyes to a treacherous, slum lifestyle that effects everyone who lives there -- it takes us on a journey that spans three decades, providing a broad, yet extremely detailed and specific examination of that lifestyle. It also shows us that it is still possible, even under such circumstances, to reach your goals.
- Eternal Sunshine of the Spotless Mind: the most genuinely human take I've seen on relationships and the memories associated with them. Fantastic performances, fantastic score, fantastic script and direction; a poignant look at romance/relationships/memory.
- Shaun of the Dead: one of my favorite comedies of the past decade and I think my single favorite zombie movie. I love how it blends so many genres that wouldn't normally fit together, but this movie makes it work to great effect.
- Oldboy: stylistically awesome, showcasing a brave performance from Min-sik Choi. Has one of my favorite twists; the whole movie has a pace and energy that adds to it's already interesting plot.
- The Fountain: open to many interpretations, this film captures thoughts and feelings about love and death that are very touching and profound. Again, great performances here, a stunning score/visuals and themes I haven't seen explored in other films.
- The Lord of the Rings (kind of cheating since there are three... but they should be considered as one long movie): epic in every sense of the word, I love these movies because they tell an archetypal story of the hero's journey in such a magnificent way. Few movies really suck you into a completely fictional world and mythology, but LotR does it with ease.