Maybe not so much online and business applied, but certainly one of the mustreads in the field of the management of small- or middle-sized organizations. Abroad often listed as a textbook on the courses on “social web/online communities”.

Moreover, Surowiecki’s “The wisdom of crowds” (http://www.bookdepository.co.uk/book/9780385721707/The-Wisdom-of-Crowds) is also an interesting one, but I guess you are familiar with it.

Ups, I almost forgot the most cited one in the academia: Preece “Online Communities: Supporting Sociability, Designing Usability” (http://www.bookdepository.co.uk/book/9780471805991/Online-Communities). Since its coming out in 2000, it has been considered as THE textbook in this field (a great part of the positive feedback was almost certainly due to the annoyance of the research community with volumes that conceived online communities as something existing “far away from the ‘real’ world” full of romanticism or postmodern personal nihilism [i.e., Rheingold, Turkle]).