Early in Season 1, Dana spent an entire episode agonizing over whether or not Lara was gay. At the end, Lara pinned her against the lockers, kissed her, and whispered "Just in case you were still wondering."
Howie coming out to his big sister Dana in Season 2.
Carmen and Shane's mutual confession of love in Season 2. Too bad Mark caught it on tape, and Jenny (Shane's best friend and roommate, who Carmen was dating at the time) saw it.
Dana's funeral in Season 3 (the real one).
Carmen's family showing up for her wedding, to her complete surprise.
In Season 2, the following dialogue happens when Kitt reopens the Planet Bette has this to say: You know, when I was a kid and I saw you on stage, I used to think "That's my sister and she can do anything." I feel that way right now.