Jusepe de Ribera, The Martyrdom of Saint Bartholomew, 1634
The homepage of the National Gallery in Washington, DC, currently features an online exhibition of paintings from 17th-century Spanish painters. In addition to the Ribera you see above, the exhibition features works by Juan van der Haben y León, Zurbarán, Velázquez, and Murillo. All these paintings are presented beautifully and are well worth a half-hour or so of your time to see.
Other NGA online exhibitions of Baroque art and artists appear below the fold.
Rembrandt's work is featured in three of these exhibitions: an in-depth study of the etching, Abraham Entertaining the Angels, and two larger exhibitions, Rembrandt's Late Religious Portraits and Strokes of Genius: Rembrandt's Prints and Drawings.
A collection of genre paintings and portraits by Gerard ter Borch
And two in-depth studies of individual works: Johannes Verspronck, Andries Stilte as a Standard-Bearer, and Vermeer's Woman Holding a Balance