My first naming scheme revolved around monkeys, I had spacemonkey, funkymonkey and.. I forget the third. That one didn't scale well.
For a short while I used characters from children's books (mom is a librarian who loves children's books), this included lafcadio, lorax and grinch.
Right now it's robots from Futurama. Bender, flexo (the Win XP dual-boot of bender, which is OSX), clamps, roberto (the crazy, stabbing robot), calculon and my dedicated server, robot-devil.
Not that anyone asked, but hey, naming schemes are fun!