At home I went for the "annying computers of SF" theme: orac, eddie, hal, holly ... Mind you, it's a good job I don't have many machines: the next name I can think of is "computer" from ST:TNG. I guess I could also add marvin and data. A windows machine was called frogstar because it was particularly stupid.
At work (a University meteorology department) we used to use cloud types (cumulus, cirrus, stratus ... ) and there are now a few other naming schemes dating from when we merged several departments into one bigger one.