Search for just about any topic in entertainment and pages from the IMDB (Internet Movie Database) will show up. It features tons of information about many movies, television shows, and celebrities.
TV Guide Online has listings for what's on the air, as well as articles and info about various shows.
For more entertainment news, I frequent zap2it.com
and scifi.com.
If you're looking for DVD information, either search for your topic at amazon.com or check the release schedule
at TV Shows on DVD.com.
Want to know what happened in a movie without actually watching it? There's a good chance that Wikipedia will have a summary of it.
If it's episode recaps you seek, Television Without Pity features detailed summaries of some of the hottest shows.
TV.com features descriptions for episodes of many, many shows.
Drew's TV Script-o-rama has - as you might imagine - links to transcripts of television shows.
If inaccuracies in movies keep you awake at night, The Nitpickers' Site is for you.
"'Scuse me while I kiss this guy"?? Find out what that song really says at KissThisGuy.com
Feed your fiction fever at fanfiction.net, where you'll find thousands of stories to choose from, conveniently grouped by topic.
Did your favorite site close and leave you with nothing but a URL? Take that URL to the Internet Archive, and you might be able to find an archived version of the site.
When all else fails, try searching on Google.