A is for Antedians. Evolved mongeese.
B is for Berengarian dragons. Never seen on screen, but huge.
C is for Cardassians. AKA Spoonheads.
D is for Deneva flying pizza monsters.
E is for Excalbians. Silicon-based, and curious.
F is for Ferengi Rules of Acquisition. There are 285 of them. So far.
G is for Giant clone of Spock.
H is for Harcourt, Harry Mudd's full first name.
I is for irritating early voice of the TOS computer.