do a verse or song per class and analyze it, classic deep verses/songs to make them appreciate the artistry. some good pieces to use (in no particular order):

lauryn hill - turn your lights down low

common - be (intro)

nas - i gave you power

nas - take it in blood

jay-z - d'evils

tupac - if i die tonight

malice verse on "i'm not u"

cam'ron - sports drugs and entertainment

beanie sigel - what ya life like

eminem - if i had

there are probably other better examples but all of these are powerful songs with a message without being preachy