I recently discovered that what seems like the entire Life photographic archive is available in digital format through the Google image search function.
http://images.google.com/hosted/life
In my previous life (before I was a PhD student), I studied photographic archives. In fact, I wrote an entire 50,000 word research paper on photographic preservation. I was also involved in Rush University’s digitization project of a part of their photographic archives. Getting to sort through hundreds (thousands?) of old pictures made the tediousness of numbering them all less painful.
Anyway, the Life image collection is really fantastic. Here are some of my favourite images I have come across* so far.
* My search terms often include “library” and “bicycle”
quaking blog 
Thanks.