(via deviantart)
For me, music and writing have always gone hand in hand.
Whenever I think of a plot line, I automatically start looking for a theme song or maybe even an entire soundtrack. Using windows media player, I repeat the song or songs over and over while I'm writing.
I don't know why I do that, but I've never actually finished a manuscript without picking at least a theme song for it. For my first manuscript, I chose Bluer than Bluer by Regine Velasquez. For the second, I picked Saving Forever for You by Nina, Smile by Uncle Cracker for the third, and I Never Dreamed Someone Like You Could Love Someone Like Me for the fourth.
I'm also really fussy about the songs. It really has to "go together" with the story of my characters, and the message of the song needs to be similar to the theme of my novel. For example, I picked Smile by Uncle Cracker because the song is about being crazy in love with someone. Well, my characters from my third novel, Dave and Grace, drove each other crazy and ended up being crazy in love with each other.
Also, having a theme song has saved my manuscripts from being deleted more than once. Having a song to listen to while writing gave me ideas for scenes and even helped me internalize the emotions of the characters.
What about you? Does music help in your writing or do you prefer silence?