I'm building a SharePoint environment that will be composed of many departmental sub-sites. Each of these sub-sites will have membership defined through Active Directory groups. I need to display on the homepage each of the sub-sites members. I need it to read and display the list of users through the AD group, is there a good web-part that fits this bill?
The User Directory Web Part from Bamboo might do this for you.
Otherwise, you can roll your own if you have development capability. There are tutorials out there to do this, such as here: http://sharepointrookie.wordpress.com/2008/07/13/display-site-members-from-ad-groups/
SharePointBoost sells several web parts for working with Active Directory including the Site User Directory part that does exactly what you are talking about. From their site:
I am NOT affiliated with them in anyway, but I like their stuff :)
There is also an opensource project on CodePlex (http://adselfservice.codeplex.com/) with a Profile Manager and a Change Password control. These don't do what you are talking about, but may be helpful and the source on the site would be an excellent place to start in looking into rolling your own. But the part above is actually pretty cheap, and it would be much smarter just to buy it or something similar unless you have very specific needs.