A recent post on The next web prompted me to pull together a bit of interesting material on WordPress, arguable the worlds’ most popular open source software for blogging and other websites. The post on TNW talks about the history and the entire ecosystem around WordPress, with particular emphasis on the commercial opportunities and legal subtleties around open source.
For a more practical overview of the business applications of WordPress I suggest you take a look at John Jonas’s video on the way he uses it. At 4 minute 50 he gives a list of use cases.
This post on WordPress Jedi links to a number of (mostly) commercial themes to do these tasks.
Finally, this link gives a step by step guide for setting WordPress up for marketing on the internet, with all the important plugins.