When picking my current naming scheme, I deliberately chose something with a large scope so I didn't run out of names quickly and with enough room to allow me to play a bit within it, giving machines appropriate names. The one I picked is the titles of "classic" computer games.
This has a huge ever-expanding set of usable names, and gives me plenty of room to have fun. My router got called frontier and my Windows desktop at work solitaire for example.
It's also allowed me to have mini-sets within the larger set, for a while I used games created by David Braben and Ian Bell (my laptop still bears the name elite), then as I replaced those I started to use rogue-like games and currently my servers are named after god games.
About the only rule I have is that a name may never be reused unless the reason for the machine is being replaced or reinstalled due to a failure out of my control.