Can anyone recommend a good book as an introduction to social media?

The New Influencers: A Marketer's Guide to the New Social Media is great jump start into the social media.

• 

  Peter Morville: Ambient Findability : What We Find Changes Who We Become

• Convergence Culture

already becoming a little bit outdated, but still essential reading:

Interface Culture : How New Technology Transforms the Way We Create and Communicate

 Steven Johnson: Emergence: The Connected Lives of Ants, Brains, Cities, and Software

Howard Rheingold: Smart Mobs: The Next Social Revolution

Disclaimer: I write for Howard Rheingold's website, and am friends with him. But anyone will tell you it's a great book on this subject. 

Thanks Sam... lots of reading for me.