Here is the list(exhaustive)–
www.linuxquestions.org
A full list of Red Hat & Fedora mailing lists –http://www.redhat.com/mailman/listinfo
Fedora forum– http://forums.fedoraforum.org/showthread.php?t=25252
Open SuSE mailing list-opensuse@opensuse.org
Ubuntu mailing lists & forums–https://lists.ubuntu.com
http://ubuntuforums.org