Esteban Murillo, un pintor al servicio de la fe
Escuela de Barbizon - Francia
Autorretratos de pintores espanoles
La vida y la obra de Peter Paul Rubens
Verano, por Joaquín Sorolla, pintada en 1904
Velazquez, Ribera, Zurburan, y Murillo
Eyes (nose, eyebrows, also) of women painted by many different artists. If you paint portraits, you'll want to see this. It's amazing how different each one is from the others.
I'm not sure how authoritative this is, but it's interesting to look at, and thought-provoking.