I found this article in the 2010 (!!) archives and have updated it. Surprisingly, the general gist is still accurate.
There are numerous alternatives for producing PDF output from DITA content. The approach you choose will depend on your output requirements—do you need images floating in text, sidebars, and unique layouts on each page? How often do you republish content? How much content do you publish? Do you need to create variants for different audiences? Do you provide content in multiple languages?
This article describes several common approaches and what requirements they support best. Your options include the following:
DITA Open Toolkit (OT)
CSS-based tools, such as Prince
InDesign
Others
DITA Open Toolkit
The DITA Open Toolkit includes support for PDF output via XSL-FO.