A is for Andorian antennae.
B is for Beta III's humanoid society, ruled by the computer system calling itself Landru.
C is for Ceti Eels. They clear out earwax like you wouldn't believe. But they have really bad side effects.
D is for Denobulan wives.
E is for Excalbians. Talking rocks. Bad idea for an alien. Unless they were just masquerading as talking rocks.
F is Federation Science Council.