After a successful campaign to liberate the English translation of the French Debian Administrator's Handbook, Roland Mas and Raphaël Hertzog announced its availability under the Creative Commons BY-SA license. You can read it online, download it for free, apt-get install debian-handbook if you're using Debian, or buy a physical copy (or donate for an electronic version). I skimmed through it, and discovered a few debconf and libvirt tricks I hadn't known about within a few minutes.