Catalog for 43 national libraries of Europe, contains some digital collections of books that are out of copyright.
An online book resource with some full text books (out of copyright) and searchable books (with snippets and page numbers).
Brill is an academic publisher with specialties in humanities and social sciences. Search with your keyword at the left under Refine Search > All. A green icon next to a title will indicate full text access.
A listing of full text books online produced by a digital library planner and researcher at the University of Pennsylvania.