Top 8, you say? Why 8? Well, unlike The Guy With The Glasses, I can't be bothered meet the quota, let alone go that little bit further. :P
So, what makes a good soundtrack? It should be powerful, able to envoke all kinds of emotions add a whole new dimension to the movie experiance. But it should also be subtle, and able to blend into the background when needed.
So, looking at this criteria, who would be worthy of the title of 'Best Composer of All Time'? (In reverse order, because otherwise it's not exciting is it? ;))
THESE ARE MY PERSONAL OPINIONS, PLEASE DO NOT TRY TO SHOVE A NEEDLE IN MY ARM AND DRIP FEED ME YOUR OPINION.

8) John Williams: One of the best known composers in history, Williams has an impressive resume, including Star Wars, Indiana Jones. He is known for his full orchestral pieces, with a heavy use of strings and brass instruments.
Notable Works: Harry Potter, Star Wars, Memoirs of a Geisha.

7) Joe Hisaishi: A frequent collegue of 'The Japanese Disney' Hayao Miyazaki, Hisaishi has won the Japanese equivalent of the Academy Award for Best Music five times, has created many memorable soundtracks for many anime films.
Noteable works: Spirited Away, Howl's Moving Castle, Princess Mononoke, My Neighbour Totoro

6) Shiro Sagisu: Born in Japan, Sagisu is known for his extremely varied score for many anime series. Using voice talent, orchestra and synths, he is able to create a thick and weightly accomplice to many different anime programmes.
Noteable works: Bleach, Bleach: Memories of Nobody, Bleach: The Diamonddust Rebellion, Evangelion: Death and Rebirth

5) James Newton Howard: With over 100 compositions to his name, James Newton Howard is on of the formost composers in Hollywood. He is famous for his fast work, and is often called in as a last minute replacement. He has been nominated for 8 Oscars, although he has not won the award yet.
Notable works: The Dark Knight, Hidalgo, Peter Pan, Treasure Planet, Dinosaur, Prince of Tides, The Village

4) Danny Elfman: With his multiple of collaborations with Tim Burton, what's it going to take for Elfman to get some love?! This is a man who deserves an Oscar if ever I saw one! He frequently combines orchestral sounds with digital sounds, and whether you remember him for his timeless Batman score, or his work on The Nightmare Before Christmas, Elfman is one of the most talented composers working today.
Notable works: Corpse Bride, Big Fish, Chicago, Spiderman, Sleepy Hollow, Black Beauty, Batman, Edward Scissorhands, Beetlejuice.

3) Howard Shore: After winning 3 Oscars for The Lord of the Rings Trilogy, people might think that Howard Shore is only famous for his epic partnership with Peter Jackson. However, Shore has also created some brilliant soundtracks for films such as Philidelphia, Easten Promises and The Aviator as well as the original David Cronenburg films.
Notable works: The Lord of the Rings, Phildelphia, Ed Wood.

2) Alan Menken: The supreme heavy-weight of the Disney musical department, Menken has scored 6 of the most beloved Disney classic. (The Little Mermaid, Beauty and the Beast, Aladdin, Pocahontas, The Hunchback of Notre Dame and Hercules) He has won 8 Oscars, 2 for Pocahontas, 2 for Aladdin, 2 for Beauty and the Beast, and 2 for The Little Mermaid.
Notable Works: Pocahontas, The Hunchback of Notre Dame, Beauty and the Beast

1) Hans Zimmer: With such a huge range of scores under his belt, who can't find at least one piece of his that they adore? After being nominated for 7 Oscars, and receiving a Lifetime Achievement Award in Film Composition from the National Board of Review, Zimmer is recognised as one of Hollywood's formost talents. He is known for including traditional cultural elements into his pieces, (the tribal chanting in The Lion King) and his seamless merging of synths and orchestra.
Notable works: The Dark Knight, Pirates of the Caribbean, The Da Vinci Code, Spirit: Stallion of the Cimarron, Gladiator, The Lion King, Rain Man