https://www.bham-lug.org/ - Birmingham, Alabama Area Linux User Group
https://wiki.ubuntu.com/AlabamaTeam - Alabama Ubuntu Local Community (LoCo)
http://www.pathname.com/fhs/ - the Filesystem Heirarchy Standard (FHS)- good resource.
http://www.lanana.org/docs/device-list/devices-2.6+.txt - the official registry of allocated device numbers and /dev directory nodes for Linux.
Mirror of http://www.dirac.org/linux/system.map/ - This has a good explanation of why the System.map file exists and how it {is, can be} useful.
Netfilter/iptables Documentation - this is the documentation provided by the netfilter / iptables project. If you're looking for an introductory tutorial, see Oskar Andreasson's tutorial.