Gabe Zichermann's new book rocks.
Game-Based Marketing: Inspire Customer Loyalty Through Rewards, Challenges, and Contests
What i like is his book is full of real world suggestions that are easy to implement instead of esoteric ideas. You know how when you read some books you think ok...but how does this apply to me - not this book, by the end of every chapter you realise hmm thats interesting i could use this example here etc.
According to this Venture Beat article - http://venturebeat.com/2011/04/14/by-2015-50-percent-of-companies-will-embrace-gamification-gartner-says of companies will use it in some form or another by 2015 to encourage interaction between companies and their users/customer and even vendors.
We used some of his suggestions on http://www.LiveBaseballChat.com so will be interesting to see how well we can execute on Gabe Zichermanns ideas