Well, music is one of my main obsessions - my mp3 player contains the pop music of the entire twentieth century - all of it - up through 2003, when my research data ended. From those scratchy gramophone charlestons of the 1920s on (the oldest one I have is recorded from an actual Scott Joplin piano roll from the late 1800s), until the Billboard charts began to issue weekly lists in the 50s, when tracking what the top tunes were becomes much easier. If it ever made the Billboard Top 40 charts, it's in there, including all those classic rock standards that were never released as singles, and anything that missed the Top 40, but became culturally significant anyway - The Waitresses' 'I Know What Boys Like' for instance only made it to #52 on the Hot 100, but the (then) new cable channel MTV played the hell out of it....uhm...sorry...toldja that obsession was one of my biggies...
Anyway, I listen to a wide range of stuff, but I do find that often one specific song will attach itself to a particular character or scene that I'm writing and sort of become the soundtrack of that part of the story - and always something that's appropriate for the time period involved. The novel I'm working on now has threads running through three generations, so there's music inspiring it that ranges from Jack Teagarden's version of 'I'll Be Glad When You're Dead You Rascal You' and Ella Fitzgerald's "I'm Just a Jitterbug' from the thirties, to Bobby Pickett's 'Monster Mash' which charted three times, though this scene is during it's second peak in 1962, to a character in a contemporary timeline who's into Tool and his goth rockabilly girlfriend who likes Elvis and Little Richard.
I got a really awesome creepy dream sequence a few months ago listening to a recording of the sounds of tree frogs at night. Dude.