I don’t normally pay attention to the background music in anime but there are just some tracks that become indelibly associated with key scenes. When I hear Salva Nos (Yuki Kajiura: Noir), I always think to myself that Kirika is going to kick some serious ass. Likewise when Foxy Doll (EDISON: Black Lagoon) comes on, the image of Revy or Balalaika strutting their stuff comes to mind. Or Haruka charging with her bass guitar to the strains of crazy sunshine (The Pillows: FLCL).
Ghost in the Shell has impressed me with all its offerings, including the Innocence OST (on order from TSRI) and the Solid State Society OST. Bought the first and second sound tracks for Stand Alone Complex for GBP 10.99 each via Amazon.co.uk (with free delivery FTW).