Yesterday, I went with Carlo Gesualdo's "Peccantem me quotidie," because I find Gesualdo's music strange and jagged (and occasionally, unsettling), much like Ash Wednesday itself. I did not go with Palestrina's, because it's much less strange. It is, however, mournful and beautiful, and well worth a listen. (Also, HERE'S the whole playlist.)
Peccantem me quotidie
et non penitentem,
Timor mortis conturbat me.
Quia in inferno nulla est redemptio.
Miserere mei, Deus, et salva me.
I who sin every day
and am not penitent
the fear of death troubles me:
For in hell there is no redemption.
Have mercy upon me, O God, and save me.