Archaeology websites: list 1 and list 2
The University of Heidelberg has digitized lots of journals and catalogs, auction catalogs, and other content.
The Association of Architecture School Librarians has compiled a list of open access contemporary architecture resources, including institutional repositories and lectures by contemporary architecture practitioners.
Many museums have put up catalogs online (some), so if you can determine that a catalog is published by a museum, there MAY be online availability on a museum's website for institutions not already noted above.
BOOK REVIEWS: Even if one can't access a print monograph or exhibition catalog, a book review of that book/catalog may be available. See a list of book review sources for art and architectural history and related here.