As I wrote 'Poisoned Rationality', I didn't have just one playlist. I was listening to a lot of different things, alternating them to catch different moods. To me, two songs scream 'Poisoned Rationality' to me. They are 'Ave Maria' by Giulio Caccini and Paul Pritchard and 'Can't Stand Me Now' by The Libertines. The former I can't listen to now without thinking about Mello from chapter 18 (Red) to chapter 22 (Abyss).
It is much easier to point to different scenes and say which song sums it up, than to create a proper playlist. For example, as Mello did his Ishtar routine during chapter 28 (In the Presense of Deity), I was listening to 'Mr Brightside' by The Killers. However, I will attempt several playlists, explaining where they should fit in. Beyond these though, assume that I was listening to a variety of things without really paying attention to playlists.