Public Relations and the Social Web is a good introduction to how the internet is destroying the media and its impact on the public relations industry.
It's a practical book that explores how public relations practitioners need to move beyond the traditional media and build relationships directly with audiences using digital and social forms of media. It's not just a well-written text but is a near comprehensive catalogue of what practitioners need to consider when planning a public relations campaign.
I recently returned to the book after collaborating with author Rob Brown on Share This, the crowdsourced social media handbook from the CIPR. Inevitably new technologies and social networks have emerged but the shake out of the traditional media remains a work in progress, and the book is as relevant as when it was first published.