The Hebrew University of Jerusalem has a big selection of historic city maps and contemporaneous artwork, in high-resolution and low, from the 1500s to the mid-19th century. Most are in Europe and the Middle East; there's a smattering of sites in Africa and the Americas.
They've also created a very attractive, free screensaver for Windows using many of the pictures. Download it here.
The image above is a detail from an engraving of Rome by Pirro Ligorio, first published in 1575.