So, I did a little research and while there are numerous free gradebooks out there - it looks like Learnboost is a nice alternative. When you log on to the site you can view the site through the eyes of a teacher, parent, or student who is currently using the site.
Embedded below is a helpful video created by Learnboost to showcase their site.
Should you have any questions, or other free gradebooks that you currently use, please let me know.
** Update ** Click here for Richard Byrne's suggestions for grade books.