Support / Maintenance documentation for development team

Question

I'm working in the Development dept (around 40 developers) for a large E-Commerce company. We've grown quickly but have not evolved very well in the field of documenting our work. We work with an Agile / Scrum-like methodology with our development and testing but documentation seems to be neglected.

We need to be able to make documentation that would aid a developer who hasnt worked on our project before or was new to the company. We also have to create more high level information for our support department to explain any extra config settings and fixes of known issues that may arise, if any.

Currently we put this in a badly put together wiki, based on an old Sharepoint / TFS site.

Can anyone suggest some ideal links or advice on improving the documentation standard? What works in other companies?

Has anyone got avice on developing documentation as part of an agile process?

Many thanks,

ben