I'd like to recommend that everybody read the new edition of Cost-Justifying Usability : An Update for the Internet Age.
I just finished reading the majority of it, and thought that it was an excellent read. While it is a "usability" book, it's a valuable resource for interaction designers also, particularly if they have to ROI activities.
In addition, there was an excellent chapter that detailed how to think about improving internal social return on investment. It was Chapter 8: Categories of Return on Investment and Their Practical Implications by Chauncey Wilson and Stephanie Rosenbaum. This was a must read chapter for anybody practicing interaction design/UCD within a corporate organization.