The big three:
UDP/137 NetBIOS Name Service
UDP/138 NetBIOS Datagram Service
TCP/139 NetBIOS Session Service
Another good one to have:
TCP/135 Remote Procedure Call
Depending on what you are trying to do across the firewall with Microsoft's products, here are two links at Microsoft's website that lists some other important ports:
How to Configure a Firewall for Domains and Trusts (Microsoft Knowledge Base Article - 179442)
http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/Q179/4/42.ASP&NoWebContent=1
Cannot Log in to Windows NT Domain Over Internet Connection (Microsoft Knowledge Base Article - 170998)
http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/Q170/9/98.asp&NoWebContent=1
Hope this helps.
