A is for Andoria.
B is for Betazed.
C is for Ceti Alpha V(I'm assuming it was in Federation space based on "Space Seed" and TWOK...not 100% sure, though).
D is for Delta IV, Ilia's home planet
E is for Earth. Birthplace of the Federation.
F is for Fillandia
G is for Galorndon Core
H is for Halii
I is for Izar