I worked for the Irish Section of Amnesty International for almost 6 years on a part time basis. During the first number of years I maintained the existing site and built many small sites to promote various campaigns and initiatives.
I built a small team of designer / developers and together with the existing IT resources in the organisation we built a completely new site using the Drupal content management system.
The organisation had quite complex needs and a significant amount of time was spent talking to the various departments, gathering requirements and ensuring that as many of the needs of both staff and membership as was possible were met.
The end result was a site that showed clear gains - encouraging activism on the part of members and also greatly increased the amount of online memberships and donations.
Departments within Amnesty were able to manage their own content on the site - allowing them to respond to events rapidly, keeping the site relevant and up to date without relying on a small and overstretched IT department.