Flubaroo is a free tool that helps you quickly grade multiple-choice or fill-in-blank assignments. Besides grading, Flubaroo also calculates average assignment score, computes average score per question, and flags low-scoring questions, shows you a grade distribution graph, and gives you the option to email each student their grade, and an answer key.
In order to use Flubaroo, you must have a Google Docs or Gmail account. I think Flubaroo is a useful tool for teachers to grade online assignment. It helps teachers get reporting and analysis on student performance as well as email scores to students.