As a social media professional, what should you be reading?

What books are you currently reading to learn more about social media? Mashable just published a list with what they believe are the top five books. What would you add?

Trust Agents by Chris Brogan and Julien Smith
The Whuffie Factor by Tara Hunt
Six Pixels of Separation by Mitch Joel
Crush It! by Gary Vaynerchuck
The New Community Rules by Tamar Weinberg

For commentary on the books, read the full article at Mashable.