Utility to Report Folder Disk Space Usag

Does anyone know of a utility or third-party application that can be run against a Windows 2000 server to provide a report of what files and folders are using what disk space? I have a server that is constantly running low on disk space and I cannotfigure out what it causing the disk space to get low. I have many folders and files on the server. I have tried many of the obvious such as temp files and so forth. Thanks in advance for your assistance. I have plenty points to give to someone that can help.