The Chemical Heritage Foundation in downtown Philadelphia has one of the best collections of science-related materials in the country.
The Smithsonian Institution has a wide variety of scientific specimens and scientific texts which can be consulted digitally.
Images from the History of Medicine contains hundreds of visual sources from the collections of the National Library of Medicine.
The Einstein Archives Online contains digital versions of Einstein's papers held at Cal Tech and Hebrew University.
Linda Hall Library digital collections, covering a variety of topics in science, engineering, and technology.
Darwin Online, a project which includes digital editions of Darwin's published works as well as manuscript materials.
The Osler Library Prints Collection, documenting the history of medicine from the 17th to 20th centuries.
The American Philosophical Society Digital Library, which contains scientific and anthropological images and manuscripts.
An exhibition on scientific illustration, Seeing is Believing comes from the New York Public Library.