Already a great Google add-on, the latest update to Flubaroo enables automatic grading and emailing of grades.
This new autograde option in Flubaroo allows the teacher to have their students automatically receive their scores after submitting their responses to quizzes created in Google Forms. Students will receive an email with their scores and (if you choose) the answer key.
To use autograding in Flubaroo, the teacher will still have to set an answer key and grade at least one submission before autograding will work. Click here for a complete set of directions on enabling autograding in Flubaroo.