The writing of Benton and its sequel would not have been possible without the hyper-reliance I have on musical leitmotifs, both for scenes and for individual characters. Spoilers follow, obviously, but here is a small selection of the tunes that I write too. Character's themes are first, followed by some comments on the music for individual scenes. The songs are either significant lyrically, musically or thematically. Ash's, for example, is musically significant more than lyrically, Benton's changes as his personality does, and so on.
Asha: Cornership's Brimful of Asha (Fatboy Slim Remix)
Mai Yamane Gotta Knock A Little Harder
Book 1: Nelson Riddle's Your Zowie Face
Ben Folds Evaporated
Book 2: David Bowie's Quicksand (1972 Demo).
Harvey Danger's Flagpole Sitta
Efah: Maroon 5 (Kara's Flowers) Control Myself
Helena: ENOZ's When I Was Love (The guitar line more than the lyrics)
The Seatbelt's The Real Folk Blues
Note: given the connections between Farose and Icelandic, I would say that Sigur Rós' Starálfur is a song that Helena sang to her children to get them to sleep.
Líadan: A mix between Dare and Wo Qui Non Coin. And when I say "mix", I mean play them simultaneously. Do it.
Min: Matsuoka Yuki's Matsutte Matsutte! Irassha~i!
MIWP: Garry Schyman's The Ocean On His Shoulders
Queen Cordelia: Ben Fold's Selfless, Cold and Composed.
Perdita: The Delagdo's The Light Before We Land
Rob: The Seatbelt's Ask DNA
Andrew Cassiel: Gabriel Faure's Requiem in D Minor "Agnus Dei"
The songs Asha heard in her head when fighting the Kapnoi are first, Radiation Fox's Descend and then, most importantly, David Bowie's Bombers.
Ash's rainy day song is, natch, Sunao na Kimochi ~Aru Ame no Hi~ Haruhi no Omoi (Obedient Feeling ~That Rainy Day~ Haruhi's Thoughts) by Satoru Kousaki,
Benton passing through the pool and back into his world, all that sequence was inspired by Mai Yamane's BLUE (You're Gonna Carry That Weight). Actually, the importance of that song to the book as a whole can not be overstated.
The scenes in the mall came about by listening to The Divine Comedy's The Lost Art of Conversation more or less on repeat, along with most of the album Bang Goes The Knighthood.