Below is my pick of film music within this span of 20 years: 1990-2009. I haven't watched all films in the list, but I did at least hear the music from the soundtracks. At least they already sound great given that they were played outside the context of the film, so I think that they will in a way work well in context (all of those that I have heard in context are really good). The list may not include the other so-called critically acclaimed original scores since my scope is way more limited than that of the critics. Basically, these are the scores that I think will stand the test of time (arranged in chronological order).
1990s:
Beauty and the Beast
The 1990's is the decade where Disney animations have many memorable songs and original scores (especially songs). Well, I consider film music from this one to be the most remarkable among the Disney/Pixar line so far.
Schindler's List
This is an outstanding example of a mournful score whether it is the version of the strings or the piano. One thing stands out: a heavy heart is involved here.
The Lion King
Speaking of African music and its contribution to the field of music, this film has made use of the African element very well. A lot of nice "folk things" can be classic enough.
Braveheart
It's the good old Celtic thing. Think about the flute and the strings and how they can pull some heart strings and brain strings.
Il Postino
This is a very good example of film music that was given an integral role in the film. If you talk about the "space between the notes", the composer indeed knew how to use this important "musical note".
Sense and Sensibility
There's not much variation in the music, but this exhibits good use of stringed instruments. It's a score, but one might like to call it "poetic".
Shakespeare in Love
It's Shakespeare so one might expect some heavy blow of romance and drama in the music, but the score in a way defies the Shakespearean atmosphere; maybe it represents the whimsical side of Shakespeare. Overall, it is a light-hearted and inspiring composition, in which one of the "Shakespearean" detractors might say, "I like this side of Shakespeare".
2000s:
Crouching Tiger, Hidden Dragon
This is one of those mournful film music played using the violin. It's a slow movement that has the capability to keep the listener engaged. It can also help you appreciate the Chinese culture together with its striking simplicity.
Gladiator
If you like something heroic, then try listening to this score. There is "new age" element in the music, and it can indeed bring you to the days of the Roman Empire. Amidst the action-packed musical ride is a nice flute sequence that lightens the heavy atmosphere of the battle.
A.I.: Artificial Intelligence
The odd combination of something mechanical and organic is well done here. Just the notion of combining both mechanical and organic into a harmonious musical sequence is remarkable enough to consider the composer kinda genius to "meddle" with "too many notes".
The Lord of the Rings: The Fellowship of the Ring
Three things that will remind me of the score -- the flute, the strings, and the voices. This is a good example of a score with multiple themes but unified successfully by the composer a la "one ring to bind them all".
Babel
This is guitar in one of its finest moments. Listening to this is like subjecting your mind into seemingly endless anticipation. Of course, it's a good form of anticipation that doesn't disappoint. It can actually motivate you to embark on taking guitar plucking seriously if you think that plucking per se hates you as a "guitarist".
Pan's Labyrinth
There have been many lullabies, but this one has some eerie feeling added to it. That's lullaby, fairy tale, and some kind of horror combined into one original film music -- that's simply not your ordinary lullaby.
Atonement
If you talk about mystery, then this is a slow mystery score. The music gives off melancholic atmosphere when played from start to finish; in fact, there are moments that can be considered "heartbreaking". Similar to the other remarkable compositions, silence has been used well in the arrangement.
I would like to mention original scores in 2010 that I consider to be more or less in the same level of regard as the ones I mentioned above:
The King's Speech
One thing is remarkable about the original portion of the score: it sounds like the music from one of the classical composers, which is really job well done.
The Social Network
It is most of the time mentally engaging, and the thing that I will remember most about the score is its hi-tech character. A lot of technical things are working for this score.
A lot of creativity is involved in these compositions, so what's next?
Maybe in the future a composer might think about including some awkward sequences, e.g. stuttering a la "The King's Speech" -- that can be challenging enough to gain some recognition.
