The meme of the moment is the New York Public Library's newly launched Digital Gallery.
Comprised of over 275,000 digitized visual materials culled from the library's extensive primary source collections, the Gallery offers the global public an unprecedented resource. Easily searched and bookmarked, anyone from the casual New York historian (the collection is heavy on materials depicting the city and its inhabitants) to the contemporary visual artist can make great use of their extensive and growing, peculiar and inspiring assortment.
I've already wasted hours strolling past the curiosities on display, and will succumb to many more I'm sure. Of particular interest thus far, is the Astronomical Atlas featuring phenomena as observed by E. L. Trouvelot in the early 1880's.
Image 1: Mars, Chromolithograph by E. L. Trouvelot
Image 2: Jupiter, Chromolithograph by E. L. Trouvelot