Artist: 1990s
Track: You're supposed To Be My Friend
Scene: Opening
iTunes US:

Artist: Richard Wagner
Track: Die Walküre: Walkürenritt
Scene: Castle's ringtone when Martha calls
iTunes US:

Artist: Annie Stela
Track: Lovesong
Scene: Castle chopping onions
iTunes US:

Artist: Amp Fiddler
Track: If I Don't (Featuring Corinne Bailey Rae)
Scene: Beckett objects to the name of the book character she inspired
iTunes US: