I love the Grammar Girl! Have you met her? She hosts a website full of quick and dirty grammar tips and her name is Mignon Fogarty. I find myself applying her advice all the time (though I doubt my editor believes that!).
Read a few articles on her site and I bet you will be surprised by how much you don't know. Her advice goes far beyond periods and commas. She gets into trends, breaking news in grammar (it is now acceptable to begin a sentence with the word hopefully--did you know it wasn't proper to do that last month?), punctuating titles and countries, verb confusion, effect versus affect, farther versus further, POV, hyphens, and sentence length to name a FEW.
To Do: The articles are short, fun, and easy to understand. I think you will love the Grammar Girl--check her out!