Whether spelling is a factor in SEO is arguable, but it is important from the point of view of user experience and having a professional site.
I have been looking for a free tool to check my whole site, and have finally found one.
It will only check English, but will look at up to 1000 pages and produces a report that is easy to follow.
There is no need to register, just an email address is required (which must be the same domain as the site to be checked) and I received a notification that it was complete after about 30 minutes.
If you would like to try it, please go here: