Johann Friedrich Overbeck, a drawing of his wife Nina, 1830. When at his best Overbeck could be a very fine draughtsman; this is superb.
Not only paintings online there but hundreds of pages of drawings! Here are a few 19th Century ones that caught my eye. First this lady with a fan by Menzel, 1846.
Also by Menzel, this undated study.
Caspar David Friedrich, a landscape in Bohemia, 1803.
Théodore Chassériau, a drawing made in Rome in 1841; if Boccherini is Haydn's wife, I suppose Chassériau might be described as Ingres' wife.