Workshop of Jan van Scorel, Portrait of a Knight of the Jerusalem Brotherhood. Circa 1540. If this was really done by the assistants rather than the master, he had some seriously talented assistants. Based on a quick perusal of what comes up in an online search, I would say that this is better than almost anything else van Scorel did; maybe the reason it is attributed to his assistants is that it is too good to be his. Whoever did it, I love it.
Francesco Maria Schiaffino, Neptune, circa 1740-60.
Giovanni Battista Gaulli, study of one of the three magi.
James Smetham – one of the original members of the Pre-Raphaelite Brotherhood – The Mandolin, 1866. Wikipedia has about twenty of his paintings, but I like this better than any of them.