Beyond the official site, Wikipedia is the most-accessed website. While there has been significant coverage regarding the accuracy of Wikipedia entries, looking up facts and figures about Hollywood is a pretty low-risk activity. If you want a quick background on an actor or a movie, visiting the social encyclopedia is a great option.
As we get closer to the awards show, one of the most popular sites on Oscar night will be the Internet Movie Database (IMDB.com). By simply typing in the name of an actor, you get a brief bio and links to all of the other movies that actor has appeared in. This is the site I use the most when my wife or a guest invariably asks, "What other movies has she been in?" or "What was the name of the movie that he was in about..."