The epigraph from Harry Potter and the Deathly Hollows is taken from The Libation Bearers, the second play of Aeschylus' Oresteia. Look at J.K. getting all literary.
"Orestes" is the name of a song by the band, A Perfect Circle. (It rocks!)
Check it out: you can get an Orestes app for your phone with the whole text of the play by Euripides.
Eugene O'Neill's Mourning Becomes Electra is inspired by the Oresteia and places similar events in post-Civil War Connecticut.