I am very much indebted to the people who've provide the wealth of information available on the internet. Some of the most useful sites are listed here.
General camera sites
Chris's camera pages taught me almost everything I know about Retinas and Retinettes, and much more.
Other camera collectors' sites
The Altix section of Dresdner Kameras has more info about Altix cameras than you would care to know about, in German.
CameraQuest's Classic Camera Profiles is probably one of the most eclectic and largest sites out there, focussing mainly on the expensive segment (Leica, Nikon, Canon, Voigtlander) but still lots of great info on other classics.
A Website about Iloca Cameras and Associated Equipment is exactly that, including some hard to find material.
Of course this list would not be complete without mentioning camera-wiki.org, the Wikipedia of cameras, and the intensely annoying, spoilt by advertising but still useful Camerapedia, if not just for the many links it provides. Tip: right-click on links and open in new tab to avoid the hyper-irritating "You are leaving Camerapedia" pop-up ads.
Matt's Classic Camera Collection has a good diversity of cameras and some excellent info how to repair the bad ones.
The Living Image vintage camera museum focusses mainly on folding cameras and has lots of sample images.
John's 35mm camera collection is a nicely laid-out site that shares some interesting experiences about collecting cameras, buying on eBay and has useful info where to get parts for that old camera desparately in need of TLC.
Mike Eckman's site contains a great photography section with detailed reviews of vintage cameras including test photos taken with those cameras, and repair info as well. Don't miss the fun vintage camera buying guide!
There are many more, some are listed elsewhere on my site, and others I'll be adding here. If you know of a website that I do not seem to know about and you think might be useful, please let me know.
Vintage camera shops
Decent vintage camera shops are scarce nowadays, as much of the trading is done at fairs and on auction sites. However, there is nothing quite like browsing through that old shop and finding that little gem (although it may cost a mint). Here are a few shops that are still going strong and I would recommend to visit if you are in the area.
Edinburgh, Scotland: Cameratiks/Camerabase. A great shop in the Morningside area of Edinburgh with a large collection of vintage cameras and lenses, as well as repair facilities. They have a lot more stuff than is listed on their website.
Ottawa, Ontario, Canada: Camera Trading Company. A lovely shop near downtown on Bank St with very friendly staff and a great collection. Particularly note the large format cameras, including one with a live street view. Speaking of which, have a look inside the shop using Google Streetview, recommended!
If you are ever in Berlin, do not miss out on the Deutsches Technikmuseum. In addition to their interesting collection of the history of TV, radio, computers, trains etc. they also have a great vintage camera collection spread over two floors. It is mostly organised by topic, e.g., cameras used for certain styles of photography, making for an interesting display.
Opening display of the Photograpy section.
The focus is mainly on German cameras, but that can be forgiven considering Germany was the centre of camera manufacture and design during the first 6 decades of last century. Some nice cut away models of lenses too.