This huge movie database allows you to search for information on films by title and actor. It provides actor filmographies and biographies, full cast and crew listings, plot summaries, photos of original movie posters, and much more.
Here is a popular film site that is fun to use. After you have found the movie you are looking for, scroll down to the section marked "Critic Reviews". There the site has collected links to reviews from professional film critics. This can be especially helpful for finding reviews of older movies.