My favorite piece of punctuation is the em dash.
The em dash is a marvelous thing—a cool pool of pause in the middle of a heated dialogue. An ounce of pensive silence in the disquiet of a teaming brain. A hiccup in the rush. It allows you to do so many things and—let’s face it—it just looks good.
With an em dash, you can pause—and then continue. You can also insert a list of things you want to include—ideas, thoughts, images, whatever strikes your fancy. There is the appositive—a noun or phrase that renames another noun or phrase right beside it—and there is also the aside—yes, that thing where I begin talking to you directly—to the audience. It can also be used to leave the reader hang—
The excellent Emily Dickinson is perhaps the most famous fan of the em dash, though her uses were anything but conventional. One might even say she “Dips—evades—teases—deploys” this thin little airborne line with effortless artistic efficacy (quote from “The Nearest Dream Recedes, Unrealized”).
Some people are not such fans of the em dash. In fact, I found quite an abundance of blogger hate for the thing. Granted, it can be overused—which is easy to do (as I have demonstrated above). The em dash should only be served in dollops. It’s like a rich bit of dessert—more than a bite will make you sick. But compared to the value it holds when wielded well, I find its misuse really a paltry price to pay.
(And, somewhere in there, I got carried away with alliteration—happens when I think about poetry!)
What’s yours?
Booknotized 
My favorite is the em dash, too! A close second is the colon.
Nice! Check back and enter your vote in the poll…I just got the kinks worked out!
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Haha. Hadn’t thought about that one. I think it’s technically a “currency mark,” but it’s tempting. Very tempting.
I like the ellipsis. You just insert it when … and it’s up to the reader