Docman is a very nice file management component for Joomla.
Docman is extremely easy to use for both the administrator and the end user. Users can easily view and download files from your website. jComments is an elegant comment solution. jComments is pretty to look at and works seamlessly with your Joomla website. XIJC is a site wide captcha program. XIJC is able to institute captcha on every user input field on your site. In order to fight spam this is a must have Joomla component."Essential Joomla Components Part 2"