Mitali's Fire Escape (YA Authors who Tweet)
ReadWriteTweet
Donalynbooks (children and YA author tweeters)
Mashable Literary Tweets
Authors on Twitter

Laurie Halse Anderson @halseanderson
Holly Black @hollyblack
Libba Bray @libbabray
Meg Cabot @megcabot
Sarah Dessen @sarahdessen
Cory Doctorow @doctorow
Neil Gaiman @neilhimself
K.L. Going @klgoing
John Green @realjohngreen
Malinda Lo @malindalo
Kate Messner @katemessner
Sarah Mlynowski @sarahmlynowski
Peter Reynolds @peterhreynolds
Sara Ryan @ryansara
Neal Shusterman @nealshusterman
Jennifer Weiner @jenniferweiner
Sara Zarr @sarazarr