The Writing Exercises website includes various types of story idea generators that are appropriate for use with any grade level.  Some of the generators include a first line generator, a random dialogue generator, or a three nouns generator.  There’s even a random image generator to get students started writing their stories.

 

Website: http://writingexercises.co.uk/index.php
Subject: Writing
Grade Level: 2-12, or any student who is doing creative writing
Price: Free