What good web file management systems do you use?

Answer 1

If you need your own file management system i would recommend http://www.alfresco.com

Answer 2

Sharepoint, just use the WSS 3.0 that comes for free with a Windows Server license.

One of the best features in WSS is document management, including versioning. Since SharePoint supports document level access out of the box, you should be able to set up a very nice system using the out-of-the-box functionality. The search functionallity also handles the item level security so if search locates documents that the current user will not be able to access, they will be trimmed out of the result set :-)