WGA - a great source for agent lists, payment scales and other information about the business of writing.
Daily Variety - a pre-eminent entertainment newspaper.
U.S. Copyright Office - for information on how to protect your work.
IMDB - to look up information about any movie or TV show.
The Source - Hip Hop Music, Culture and Politics.
Indie Talk - Independent Film forum.
Word Player - for interesting screenwriting info.
The Black List - a way to get your work seen.
The Screenwriter's Path - a great handbook on how to write for the screen - from idea to script to sale.