United States Census Bureau

Can give you ideas about people - that's where much of my Character Creator data came from. Also has loads of economic data, etc.

Google Maps

Excellent for writing about real locations and utilizing to get a visual reference for the layout. Now, with the street view options, you can almost visualize your characters into a location.

The Snowflake Method

Randy Ingermanson's theory on developing fiction as a series of building blocks.

oneword

Site provides a single word every day as inspiration for a free writing exercise. Can help to practice quick storytelling as well as provide inspiration against writer's block.