I've had various naming schemes at employers. One, it was sea creatures (the name of the company was The Pond). Another, military aircraft (the owner was a vet who spent his Army years flying helicopters). Another, the staff picked so it was a mishmash, though our SpamAssassin cluster used names of successful US presidential assassins (though when we got to McKinley's and couldn't spell it, it was marking the end of the meme). Yet another, trees.
For my personal stuff, though, I use names of famous dogs, and I try not to recycle them. I've used Toto, Fido, Speck, Einstein, Astro, Scooby, Nipper, Laika, Strelka, and a lot more. My latest are Gromit (can't believe that in 10 years I'd never used it!) and Petey.