What is your machine naming scheme?

I've ended up with a number of machines on my network, and a need to name them all in a somewhat logical way. For several years I had them named after the planets, which worked well until the PCs for myself, my girlfriend, servers and Raspberry Pi's quickly summed up to more than the eight planets. I've broadened it somewhat to include any Greek/Roman mythological figure, but the system is definitely not as clean as it used to be.

Do you have a coordinated naming theme for your machines?