Depends. For instance if you're running Fedora there's a lot of links on their site about SELinux (
http://fedora.redhat.com/docs/selinux-faq/), OTOH nothing beats dead trees like for instance Prentice Hall's "SELinux by Example". On top of that it has a *blue* lightsaber on the cover. Gasp! What a striking and valuable addition to your coffee table! Amaze Your Friends and Be The Centre Of The Party, just by showing them A BOOK! :-]