I strumbled across the Elgin Watch Collectors site, which is quite impressive and usefull for collectors of vintage (Elgin) watches. Especially when you need to indentify a certain watch when you found one on eBay or at a watchfair. Another useful link on vintages watches is Paul’s site on Gruen watches, although it is more about history on Gruen watches. If you are looking for a nice affordable vintage rectangular watch, those two brands (and thus websites) might come in handy.
Vintage Zodiacs is another site on vintage watches you might like to visit. The navigation is a bit odd (through the pulldown-menus), but it contains a nice collection of images and information on vintage Zodiac watches.
If you need a list of online dealers for vintage watches, check the dealer pages at Chuck Maddox’s site.