Conferences for IT Professionals
http://macadmins.psu.edu/conference/

Online Mailing Lists for IT Professionals
Mac Client System Administration:
http://lists.psu.edu/archives/macenterprise.html
http://lists.apple.com/mailman/listinfo/remote-desktop
http://lists.apple.com/mailman/listinfo/client-management

Mac Server Administration:
http://lists.apple.com/mailman/listinfo/macos-x-server
(less so)
http://lists.apple.com/mailman/listinfo/remote-desktop
http://lists.apple.com/mailman/listinfo/client-management

Package Making:
(quite advanced) http://lists.apple.com/mailman/listinfo/installer-dev