In the companies that I work with, Active Directory and Firewalls are often said in the same sentence, this KB article discusses the essential network ports; protocols and services that are used by Windows client and server operating systems; server-based programs and their subcomponents in the Windows server system.
I have found this document to be invaluable when it comes to making Active Directory and other Windows components such as (DFS-N and DFS-R) work through a firewall.
One of the reasons that I am adding this post is that this KB article is constantly evolving and in the pass 6 six weeks alone I have seen 4 versions.
30th March 2010 Version: 42.0
9th April 2010 Version: 43.0
23rd April 2010 Version: 44.0