Van Der Weyden's Crucifixion Diptych at the Philadelphia Museum of Art. Made for a Carthusian Monastery, it is one of the starkest paintings of its type I've ever seen. In person it actually takes your breath away.
The Opening Chorale to Bach's Matthew Passion. I couldn't find a Youtube recording of "Ach Golgotha" that I liked.
*I was going to write a longer post about how Bach's St Matthew Passion is a masterpiece of Baroque-era sampling (Bach re-appropriates tunes liberally, not just in the Chorales). But it was a stretch, and has been said before.