I dunno, I guess just songs that get me down and don't seem to really fit with the joyous occasion of birth.
We have all our music on our Ipod, and Dh and I can have some very different tastes in music. Some of his stuff I find quite depressing, other bits I cannot stand. In labour, I listened to it all. I scanned through everything and was surprised as to what I needed to listen to to get me through. (music genres covered on our Ipod: rock, alternative, protest music, heavy metal, metal, pop, and more)