Strong thing it is Samba server acting as PDC. Managing users via POLEDIT is quite easy and powerful.

For larger school networks looking to seperate the student traffic from the teacher/staff traffic add another network card and you are ready to go. (You can also do this with wireless networks or VoIP data)

PPTP VPN and Content Filtering our my two favorite. One of my clients is constantly expanding to more campuses. They have a multitude of site licenses that require access to servers at different campuses and being able to do this within minutes AND without another piece of hardware really impressed them.

OpenLDAP has been great to be able to use for SSO in their various apps.

Adding something of the equivalent of RIS in Windows Servers--There was an open source solution I used in the lab some time ago but it's name escapes me. Client Management items like RIS would be a huge value added feature.