1) The National Library of Medicine has released scans of some of the most beautifully illustrated science books - You can literally "turn the pages". Once only available by visiting the Library, you can now check it out at home.
There are only a few books, but they include Robert Hooke's Micrographia, one of the first descriptions of microbes; Vesalius's book on human anatomy, with some of the first drawings of physiological mechanisms and associations; and other medical texts from the 1400s and 1500s!
Medieval medicine in its artistic glory. The very foundations of everything we know about the human body, laid to bare in those pages.
If you don't want to flip through the books, they offer galleries of the images in them as well.
2) To celebrate 350 years, the Royal Society of London has published 60 of its most trailblazing papers online. They include the 1667 descriptions of blood transfusion and artifical respiration, the original paper on smallpox inoculation, the discovery of aspirin (originally dried willow bark from which acetylsalicylic acid was synthesized 130+ years later), Benjamin Franklin's kite flying experiment, and many more very interesting scientific accomplishments.
The PDFs are free to download and browse, and they even provide some historical perspective. Stop by the Royal Society's Trailblazing site.