I recently discovered the Digital Galleries on the New York Public Library website. It's an amazing collection of scanned prints, photographs and artwork. With over 700,000 images, I could easily spend hours getting lost in these galleries looking around. You can too by going here: http://digitalgallery.nypl.org/nypldigital/index.cfm
These are a few of my favorite images from the 'Turn of the Century Posters' gallery.
And these are just a handful of the lovely scans found in the plant gallery.