Ian Christian has added a new post to his blog today showing how you can create a custom form field type in Symfony 2 by extending the AbstractType.
I am finally starting to dive into symfony 2 properly. Yes - it's taken a while, work has taken me in different directions! I found myself needing to create a custom form field type pretty quickly, but couldn't find much in the way of documentation to do so, so I thought I'ld throw it up here; partly to help others, but mostly to get feedback to make sure I'm not approaching this from the wrong angle.
He includes the code that creates his custom "Person" model and the class to create his "transport type" select box that pulls in its values from a "choice list" class. He registers it in his bundle and it can then be included in his buildForm() method just like any other form field.