The Rijksmuseum in Amsterdam invites you to compare Caravaggio and Rembrandt. For an overview of Rembrandt's work here are Rembrandt van Rijn: Life and Work and A Web Catalogue of Rembrandt Paintings. For Caravaggio there's caravaggio.com which makes use of the Italian website Tutta l'opera del Caravaggio.
The Vinkhuijzen Collection of Military Costume Illustration has drawings of uniforms and regimental regalia from all over the world. Assembled by one of these great, eccentric collectors of the late 19th Century, Dr. H. J. Vinkhuijzen, a Dutch medical doctor who started out as an army physician and eventually rose to the position of official court physician to Prince Alexander of Netherlands. He pulled plates out of books, colored in black and white drawings and painted his own watercolor illustrations. His collection includes pictures of the soldiers of many different nations and eras, from military superpowers like the Roman Empire, France and Great Britain, to lesser known, but no less formidable forces, like Byzantium and Persia and even taking in such minnows as Luxembourg, Monaco and Montenegro. Due to Vinkhuijzen's unusual classification system it can be hard to find some of the more interesting images, such as pictures of Etruscan cavalry, Spanish military musicians and 1830's Belgian ambulance.