It's a recurring thread topic.

My bronze 1984 Trek 520 tourer "The Bronze" - a TV reference.
My blue Peugeot Mackenzie mountain bike is "Bix" because it's a beaterbike.
My red Raleigh Century is "Rubeus" because it's twice as heavy as a normal bike.
I've been looking for a suitable name for the old silver Panasonic roadbike I commuted on for 12 or so years - maybe Godzilla or Mithrandir or something.
I have a green Bike Friday on order and I'll need some inspiration there too.