Customer (or an advocate of some sort).
Basically, someone that can say, "Yes, you're building what I want and it's going to solve my problem." or that the team can go to when they have questions about how something is supposed to work. That may or may not be the same person that is doing Project Management.
Also, you're missing out on a QA person there. You can't really depend on the developers to adequately test - they're usually too close to the code and the normal response for developers is to test happy path stuff, not doing weird crap like copy pasting War & Peace into a textbox and seeing what the application does.