This might be of interest, especially to Luftwaffe buffs. If you go to the ebay.de siteenter the words foto and flugzeug in the search bar, and hit enter, you get a large number of photos which are up for auction. A lot of them are photos of crashed or destroyed planes taken by German soldiers, but there are lots of images of German aircraft in service, too. You don't actually have to *buy* the photos, you can "right- click, save-as" and put them in your "My Pictures" folder. The sellers typically mark the images up a bit ("Kopierschutz" is popular) to prevent them from being published elsewhere on the Internet, but this doesn't usually detract from their usefulness as modelbuilding references.
Does anyone know of similar sites, especially for Russian aircraft (I know about avia-n-aero already, thanks!)?