I allways name my first ship "Acheron", the rest becomes a word association game.
It could go:
Acheron (AKA LV 426)
Nostromo (The ship landing on Acheron in Alien)
Demeter (Oddly, the ship I thought it should be called - the one carrying Dracula to London)
Poseidon (Ships? Need a sea god then...)
Styx (Another river of the greek underworld)
Hades (Greek underworld, doh!)
Niflheim (Norse mythology underworld)
Valkyrie (Norse mythology chicks)
and so on and so forth.