For the past year, the San Diego Air & Space Museum has been posting images on Flickr at
http://www.flickr.com/photos/sdasmarchives/ . They have over 100,000 aviation related photos, and in most cases the images are unique to the Internet. This is an incredible site, and is easy to search. Unfortunately the images are all small and of disappointing resolution.
However, their recent set of uploads, a collection of over 1800 images relating to the Ryan aircraft company and it's people and products, was done at higher resolution (1024 pixels wide).
While this is good news for the future, it is bittersweet news, as I doubt they will be re-posting the 100,000+ images that are already posted at low res. In order to view the higher resolution images you must be a Flickr member. Basic membership is free. Once you have logged in, click on an image to open it's dedicated page. Then right click on the image and select "original size".
Flickr is a huge source of aviation images of all kinds. Although many present day airshow and museum pictures are posted, there are numerous members who have uploaded great collections, including famed aviation photographer William T. Larkins, who has made available much of his massive collection of original photos dating back to the 1930s. See
http://www.flickr.com/photos/34076827@N00/ .
Enjoy!
Shaun