Links
I usually just post a link (the famous "Here.") Of course, then I get grief for simply pointing to someone else's writing. ;)
I post quotes other times. Sometimes I will post a complete piece, especially if I'm commenting on it bit by bit, but usually things in the public domain like Presidential speeches and the like.
To be honest, I have posted entire newpaper articles in the past, so I'm not without sin here.
I am particularly careful about not reproducing items from subscription-only or other paid sites.