The Internet Movie Database: Everything you want to know about virtually every film ever made.
Mymovies.it: Il cinema dalla parte del pubblico: A major source of information about world cinema in Italian. It claims to have information somewhat analogous to what one finds on IMDB on all films from 1895 to the present. You can also purchase films and download them. Its search features are quite user-friendly and rapid.
The official site of the major Italian film studios (in Italian).
Cinema Magazine (Rivista del Cinematografo)
Internet version of Rivista del Cinematografo (Cinema Magazine), originally founded in 1928. It appears to replace Banca Dati del Cinema Mondiale, no longer available online, as the most useful Italian language site for information that is not available anywhere in English - or perhaps in any language. There are numerous short reviews of even "minor" films as well as essential cast information.
Major Italian film journal (in Italian).
Internet Bookshop Italia
A very useful Italian source of Italian films on video and DVD, frequently at significantly discounted prices (in Italian).
A very useful research tool particularly because of its archives. It includes texts and film clips (in Italian).
This is the Italian RAI TV "on demand." With a broadband connection you can download films, film clips, TV programs, documentaries, news programs, horoscopes, sports, etc.
World Festival of Italian Films (Italy)
Another extensive American source of Italian films on video and DVD.