Open Source as a business done right: SugarCRM
OK, I admit that I don't know how much revenue the SugarCRM people are making, but based on how often they make major system improvements, the look of their web site, and the services that they offer - I bet that they are doing OK.
Could SugarCRM be better? Sure, it could be written in Java instead of PHP :-)
While I also use PHP and (lately) Ruby on Rails, I just don't yet have the warm feeling of solid-ness for large scale web applications that I get with the subset of the J2EE stack that I usually use.