Check out The English Teacher's Friend collection of 1000 Writing Prompts CD (6 powerpoints with 180 prompts--one for each day of the year for 6 years or grades 6-12
Ralph Fletcher's site on writer's notebook
Creative Writing Prompts.com is a site with 365 writing prompts. Let students (as a class) pick a number from this page and go with it.
The Writer's F
older
All drafts and important grammar lessons, rubrics, etc. can go into this folder. Use it also as an idea generator.
The first time you hand them out have students spend 10-15 minutes drawing images, making a timeline of their life. This gets the creative juices going.
Then, tell them to choose one image or moment and write about it.
Here are some things you might want to keep in the folder for reference in addition to all their drafts:
One Page Grammar/style issues
Ideas Rubric
Student Version of Six Traits Rubric
Proofreading Marks