Honourable mentions: Hook, Harry Potter, Return of the Jedi, Temple of Doom, catch me if you can

10. Superman
9. Schindler's List
8. Saving Private Ryan
7. Close Encounters
6. Jaws
5. Jurassic Park
4. E.T
3. Raiders of the Lost Ark
2. Star Wars
1. The Empire Strikes Back

OK I'll bite...I doubt anyone would agree with any of these rankings, but they're mine.

1. Empire Strikes Back
2. Revenge of the Sith
3. Jurassic Park
4. Temple of Doom
5. Raiders of the Lost Ark
6. Return of the Jedi
7. Last Crusade
8. E.T.
9. Attack of the Clones
10. Schindler's List

I don't know about "best" but here are my favorites and the themes or aspects that indicate why:

1. A.I. Artificial Intelligence (Monica's theme)
2. Star Wars: Episode II - Attack of the Clones ("Across the Stars" and "Zam the Assassin/Chase Through Coruscant")
3. Star Wars: Episode V - The Empire Strikes Back ("Yoda's Theme" and "The Clash of Lightsabers")
4. Indiana Jones and the Last Crusade (Grail theme)
5. Star Wars: Episode I - The Phantom Menace ("Anakin's Theme" and "Duel of the Fates")
6. Close Encounters of the Third Kind (The musical exchange in the final set piece)
7. E.T. the Extra-Terrestrial ("The Beginning of a Friendship" and "Escape/Chase/Saying Goodbye")
8. Indiana Jones and the Raiders of the Lost Ark ("The Map Room/Dawn" and "Desert Chase")
9. The Terminal (Navorsky's theme)
10. Harry Potter and the Prisoner of Azkaban ("A Window to the Past")

Honorable mentions: 1941 (March), Jaws ("Montage" and barrel chase theme), Munich ("Avner's Theme")

Fun little exercise but hard to separate the music from my considerable emotional investment in the cinematic counterpart.

CoGro, your seemingly definitive list seems copied from a Boston Pops concert program circa 1993 with the exception of an oddly placed Saving Private Ryan. Ryan, to me, represents a Spielberg allowing Williams to not worry so much about catchy and easily hummable melodies in his music which I think represents a major step forward in the maturation and increasing interest value of their continued collaboration.

C'mon, which scores do you really like?

I would not have known to reference such a program.

Empire, to me, is the best film score in cinema history. It's powerfully thematic (Imperial March, Yoda's Theme, Han and Leia), incredibly smart and subtle (the vocals in the approach to Cloud City reference the Siren's song, foreshadowing the impending doom facing our heroes), and tightly edited. Every note has a purpose and every track tells a story.