The LIFE photo archive
The LIFE photo archive can be accessed online from now on. Google is hosting “millions of photographs from the LIFE photo archive, stretching from the 1750s to today. Most were never published and are now available for the first time through the joint work of LIFE and Google.” 
Most of these images have a pretty good resolution – at least when it comes to images on the web.
Follow this link and have a look at the LIFE archive.