DocMan is one of the best document management systems on the web. And, the good news is that they now have a Joomla 3.0 version released. This allows our websites to take advantage of the new features of Joomla 3.0 as well as the new power incorporated into DocMan.
DOCman 2.0 is a document and download management solution for Joomla. DOCman makes offering downloadable documents on your Joomla site a breeze.
Manage documents across infinite nested categories, give users permission to upload, download or edit documents, store documents locally or remotely, and prevent direct linking using the built-in anti-leech system.
Check out the overview at http://www.joomlatools.com/extensions/docman/overview.