Here are a few of my favorite blogs devoted to grammar, punctuation, and style. I know it's Grammar Day and not Punctuation and Style Day, but good writing requires all three, and they are deeply intertwined.
SPOGG: The Society for the Promotion of Good GrammarFounders of National Grammar Day.
Mighty Red PenA little bit of everything, from
punctuation issues in the news to
zombie sightings.
The Blood-Red PencilWriting advice from 19 professional editors, including Maryann Miller, who used to lead the Nebraska Novelists group until she up and moved to Texas.
The Sentence SleuthFeatures "Criminal Sentences," in which she passes sentence on sentences so poorly written they ought to be criminal. (Like the one I just wrote.)
The Grammarphobia BlogAnswers to reader-submitted questions about grammar and word usage.
The Engine RoomPokes fun at errors and oddities found in the wild, including signs and news headlines.
Apostrophe AbuseThat's right. A whole blog devoted to signs with prominent apostrophe errors. Go on, laugh at other people's mistakes.
Daily Writing TipsAs expected, offers daily writing tips, and also hosts a short story competition.
Pro Writing TipsBacking away from the minutia of grammar to give writing advice that will help you develop your own style.
Evil Editor He takes your query letters and synopses and burns them with his laser eye-beams, then mocks your plot mercilessly. Find out what it is that makes an editor heave your manuscript into the fire without even reading it.