Metropolitan Museum of Art hosts free online art history texts. Today, I revisited that collection and discovered that it has expanded to 390 volumes. All of the books can be read online or downloaded as PDFs (warning, some of them are massive files). You can search through the catalog of books by thematic category, format, and publication type. And, of course, you can search through the books by title, author, and keyword.
Applications for Education
The Metropolitan Museum of Art's collection of art history books could be a great resource for art teachers and their students. Students who are researching artists and or art movements could consult the collection to find reference materials.