Commercial search engine for locating reviews from diverse sources; it covers classic and contemporary American and international films.

The Moving Image Source Research Guide is an annotated and regularly maintained database of more than 400 of the best moving-image related resources on the web, ranging from scholarly and popular journals to film-related libraries and archives.

The encyclopedic database includes information about contemporary and classic American and international films, videos, and television shows. Entries for titles and people include credit information, summaries, awards, release information, and some professional reviews.

Database of ephemera held by the Pacific Film Archive. Search for specific films or documents, and view the digitized portion of the collection.

Covers all aspects of film sound, including glossaries, articles on particular movies and genres, links to additional resources and more.

From the National Museum of the American Indian. Portal to resources on Native media, including video, radio, tv, etc. Includes interview with practitioners and information on films screened by the museum's Film and Video Center.

From the Library of Congress. Watch and find information on 21 films and 2 fragments created 1900–1921.

From the University of Alabama. ScreenSite facilitates the teaching and research of film/TV/new media and is designed principally for educators and students.

The Media History Digital Library digitizes collections of classic media periodicals that belong in the public domain for full public access

Not the easiest to search through, but contains film reviews back to the early 90's. You can try using this pre-populated Google search that limits to Rolling Stone's site.

The publication has been reviewing all forms of media for decades.

From AMC.