Scholastic and Expo have partnered together to create the Expo Writing Resource Center. The Expo Writing Resource Center offers lesson plans for teaching writing. The lesson plans are organized into four groups based on grade level. Each lesson plan includes PDFs of printables to distribute to your students. While the lesson plans are free, Expo is obviously trying to sell more markers because they give directions for color coding various aspects of the lesson plans.

Applications for Education
The free lesson plans offered in the Expo Writing Resource Center cover all grades K-12. There are lesson plans for teaching creative writing, persuasive writing, and vocabulary development.

Here are some related items that may be of interest to you:
Imagination Prompt Generator
Two Sources of Writing Prompts
Write Rhymes Provides Fun Times