If you are looking for antique maps online, and would like a great source, check out the Perry-Castañeda Library Map Collection, hosted by the University of Texas at Austin. It’s one of the premier online map collections (and it’s free) and it covers areas around the world, and it includes maps that date back pretty far. The formats are mostly in JPG and GIF graphic formats (easily viewable through any browser). Most of the maps are in the public domain, so you are free to copy (see the FAQ for more details).
If you can’t find a map you are looking for, they have an extensive directory of links to other map sites online, as well as map dealers.