Idea Jogger : these weekly writing prompts will help jumpstart the writing process when the page remains blank. Archived topics are also available.
http://www.writersdigest.com/writingprompts.asp

Pick a Grade Writing Prompt: Select your grade level for an appropriate writing prompt and exercise.
http://tusdstats.tusd.k12.az.us/planning/resources/writprompt/top_nav2.asp

Story Starters: These story starters for elementary students offer three different prompts in each series, with text, visual, or auditory prompts. They also include writing rubrics for each grade level.
Writing Topics: This site offers several brief writing topics, all categorized by grade level.

http://www.lessontutor.com/jmstorystarters.html

Bright Ideas for Writing : For elementary classes, find writing exercises here for all genres, including opinion and persuasive essays, writing instructions, stories, or personal narratives.

http://www.eduplace.com/kids/hme/k_5/brightideas/

Yearly Writing Program: Select either single paragraph topics for elementary students or five paragraph essay assignments for older classes, and find a year's worth of writing exercises here.

http://www.teachersdesk.org/topics/par_week_program.html

Creative Writing Worksheets: These story starters come in printable student work-sheets, and should appeal to upper elementary through to middle school students.

http://bogglesworld.com/creativewriting.htm

Scroll down for numerous story starters, opinion prompts, or narrative ideas.

http://www.creativity-portal.com/becreative/activities/writingprompts.html