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.