I usually have a playlist for my muses, but it also depends on the mood I'm playing. I also select songs based on lyrics, which is why my journal profiles and the first post on their journals feature songs.
Gabriel: - I don't really need music for him, but I pull up any Tears for Fears track if the fancy hits me.
Kohran (aside from her cuteimagesongs -- Sakura Wars is a huge musical in itself after all): - upbeat JPop or KPop like STEP (KARA) or Hot Summer (f(x)) - 80's Kylie Minogue songs, specially Wouldn't Change a Thing - and whimsical things that make me think of her energy and her environment, such as a stage: Show Me How You Burlesque (Christina Aguilera).
Ryo has the derpiest playlist which not only includes OST from his canon, but mostly power pop songs from the 80's and 90's; but like Kohran, I just picked tracks out that remind me of his energy: - Through the Fire (Larry Greene) - Poppiholla (Chicane) - Deep Breath Deep Breath (Lotus Juice -- Persona 3, yay!)
Rekineeded music while I was writing her app and she's more driven by lyrics. Lene Marlin albums did the trick; but aside from those: - Whatever It Takes (Lene Marlin) - Too Late (Carole King, covered by Amy Grant) - I'm Still Here (Vertical Horizon)