Can Teach
Can Teach: Writing Prompts and Journal Topics
This site has hundreds of writing prompts/journal topics to get students started writing. Topics like "what is" and "what if" will get students thinking about what they could write.
Other
Web Worksheet Wizard: Narrative and Descriptive Prompts
Come and check out this list of narrative and descriptive writing prompts. These can be used as springboards for your writing.