The Internet Movie Database. uk.imdb.com
This Web site serves as the ultimate argument-settler for anything concerning movies. The database holds exhaustive details of plot, actors, reviews, directors, awards and remakes for hundreds of thousands of films. I've no idea what madmen and women were responsible for harvesting such details, but it works.
Tapping in the title of the re-released Frank Capra classic It's A Wonderful Life brings up a plot summary, cast list, list of Oscars awarded, a selection of dialogue from the screenplay, trivia about the original production, details of the locations used to make the film, publicity posters from the 1946 release and lists of who was involved in the production and distribution.
This information is all cross-referenced, so if you click on the name of the star of the film, James Stewart, you enter a new realm of information about the actor and all his other films. Even the extras who weren't given credits in the film are listed here, with cross-references to all their other bit-parts in long-forgotten Forties films.