A is for Asseton Assimilators.
B is for Beltane IX.
C is for Cardassian Armor.
D is for Denebians.
E is for the energy barrier that marks the edge of our galaxy. Encountering it can be a shocking experience.
F is for Frank, young Jim Kirk's uncle. In at least one timeline he was a rude jerk.
G is for Gorn, or Garak, whichever wasn't cited before. If both were cited, then is for Genghis Khan, who killed Surak.