I once came up with a great name for a product I was hacking on with my roommate, so we used that name internally. By the time we'd been coding for a few weeks, though, what the product actually was had evolved and the name was no longer relevant (despite being scattered throughout the codebase, the github repo, the directory structure, etc).
Ever since then I've been a codename fan. I go for liquor names (since I work at home across from the booze shelf)- I'm currently building Frangelico.
I generally use either the first thing that pops into my head (sometimes it's just obvious) or the song I'm listening to at the time, either name or a snippet of lyrics. SteelBreeze, ClubThing, Tain, Ronin, Arienette, etc. Works wonders.
Characters from Bananaman. Not my choice, and I can't wait for the list to exhaust... though I like the idea of calling the devs VM test server 'zookeeper'.
When I was with HP calculation division in the early 2000s, the project names came from Star Wars / Star Trek characters. Why? Because with we were working SciFi (SCIentific FInancial) calculators.
I use coffee shops or espresso company names, often local to Seattle. The list is quite limitless. Zoka, Vivace, Rococo, Velton, Olympia, Lighthouse, Ladro, and so on it goes.