I think that I would have to include The Beatles' "Revolution" as a soundtrack for when the animals take over the farm. The idea of these animals rioting and essentially chasing the humans off of the farm has an energy to it that the song captures. Following that, when the animals rejoice at being in control, I would punctuate it with, again, The Beatles', "All You Need is Love," for it is a moment in which there is a universal consciousness of success and empowerment that all the animals share in being at that moment. I would use The Who's "Won't Get Fooled Again" for the final scene. When the animals looking inside cannot fully comprehend who is human and who is pig, I think that Daltrey's anger and intensity in, "Meet the new boss/ same as the old boss" is both a statement of sarcastic observation and detached melancholy that Orwell would find appropriate.
In terms of soundtrack usage for specific characters, I would use the first track of Shore's soundtrack for Gangs of New York, entitled "The Five Points" to convey elements of Napoleon's characterization. There is a darkness and brooding within it that captures the leader of the pigs, fairly well. For Snowball, the bombing score from Pearl Harbor would really hit home. It captures Snowball's sense of sacrifice and his honor in a setting where it was not validated. Finally, the track "Lux Eterna" from Mansell's Requiem for a Dream would be brutal and intense to increase the emotional timbre of the moment in chapter 7 when Napoleon orders the public confessions and public executions of the animals. From the optimism of The Beatles to the despair of Mansell, this would captures the range of political change that Orwell seeks to illuminate in the novel.