Here are some recent additions to my list of free resources. Definitely worth a look …
From Romance University, two very informative and useful posts about choosing and using an editor.
http://romanceuniversity.org/2013/03/01/tips-before-hiring-an-editor-with-donnell-ann-bell/
Free software, including a Word plugin. I haven’t used these yet, so can’t recommend, but they look very interesting.
http://prowritingaid.com/Free-Editing-Software.aspx#.UT31pFfTNw7
http://prowritingaid.com/WordPlugins.aspx#.UT31rlfTNw5
Protecting your family’s rights to your creative product, from a major author
http://files.neilgaiman.com/SIMPLEWILL.pdf
Two good posts about common errors. I agree with the first, but think authors still need to be more careful than most.
http://news.yahoo.com/7-bogus-grammar-errors-dont-worry-060000215.html
http://www.dailywritingtips.com/10-classes-of-careless-usage/