I'm glad I'm not the only one! It usually depends on the type of genre I'm trying to write -- though generally classic rock ballads and songs with lyrical depth and focus tend to work best for me, such as Led Zeppelin's Achilles Last Stand (nothing like ~11 minutes of Robert Plant singing about youthful adventure to spark creativity). Recently though I found the song Far Away by José González, which is exclusively acoustic guitar and haunting vocals, and always seems to get me into the mood to write.

[hider=Achilles Last Stand by Led Zeppelin]
[youtube]https://www.youtube.com/watch?v=nlRjjGc6pJA[/youtube]
[/hider]

[hider=Far Away by José González]
[youtube]https://www.youtube.com/watch?v=ZO1SGvFSgZQ[/youtube]
[/hider]