For my birthday present to myself, I’ve picked up a copy of the Debian GNU/Linux 3.1 Bible. I’ve only read up to page 9, but I thought I would give it a whirl. I got a free copy of Knoppix and the Debian installation CD as bonuses.
I was going to pick out something more distro-independent, but this will be a good middle ground for me. If I decide later I want to test for an LPIC or something, I’ll get something more preparatory.