Almost 16,000 journals are indexed in DOAJ. They cover all areas of science, technology, medicine, social sciences and humanities. Since many of the titles are in languages other than English, you may want to use the "Languages" filter.
"The Digital Press hosts and publishes journals, conference proceedings, books, and textbooks in disciplines represented in Iowa State University's curricular and research programs. Materials published through the press are open access upon publication."
The Open Textbook Library provides an easy-to-use interface for locating and evaluating OER. Along with peer-reviewed textbooks, the OTL provides reviews from faculty who have adopted their texts for courses.
This is a subset of the full JSTOR collection, limited to content found in the JSTOR Open Collection. It is primarily a collection of book chapters, but it also contains several thousand freely-accessible journal articles.
Hosted by the University Library Digital Collections, the Fashion Plates collection (1776-2003) contains plates of general fashion dating back to the 18th century and continuing through the 20th century.
You can also use Google Books to look for free online books or for-sale copies of e-books. Non-copyrighted materials are a strength of their collections.
The Open Educational Resources (OER) Commons currently includes open educational materials in broad subject areas. Materials include lesson plans, textbooks, activities, assessments, readings, and more.
"The primary aim of DOAB is to increase discoverability of Open Access books .... The directory is open to all publishers who publish academic, peer reviewed books in Open Access and should contain as many books as possible, provided that these publications are in Open Access and meet academic standards"