Animals. Always animals. We usually decide based on what the robot looks like. Awesomeness of the name seems to be directly proportional to robot performance.
Starting in 2007:
Tubasaurus
Ball Frog
Luna Beast (or Balrus)
Hammerhead (or Ball Shark)
G-Wrath
Kracken
Our 2007-2010 robots (left to right):
http://www.chiefdelphi.com/media/photos/34912