A is for USS Adelphi, involved in the notorious Ghorusda disaster sometime prior to 2366.
B is for Boy Genius: Wesley Crusher.
C is for Crystalline Entity.
D is for Data, our beloved android.
E is for Elementary, My Dear Data.
F is for Farpoint Station.
G is for Gregory Quinn, high-ranking admiral at Starfleet Command
H is for Haliian, an oft-forgot species from the latter seasons.
I is for Iconian Gateways.
J is for Jarada, an insectoid species.
K is for Kling. Originally meant to be the name of the Klingon homeworld, later demoted to a probable district in the main city.
L is for Lal.
M is for Mok'bara, a form of Klingon martial arts and meditation.
N is for Nebula-class vessels.
O is for O'Brien
P is for Picard, Jean-Luc
Q is for Q, naturally.
R is for Romulans. We're back!
S is for Selay
T is for Tamarians, of all the myriad T-races perhaps the most distinct and memorable.
U is for Under Borg influence
V is for Violent telepathic rape.
W is for Worf.
X is for the oddly-named Xendi Starbase 9.